B8BAB0 (ORF OsI_29064) is a BURP domain-containing protein from rice (Oryza sativa subsp. indica). It belongs to the PG1beta-like subfamily of BURP proteins, classified by PANTHER (PTHR31458:SF2, Polygalacturonase 1 beta-like protein 2) and containing the InterPro PG-associated BURP domain (IPR051897). The protein is 623 amino acids long, with an N-terminal signal peptide (residues 1-21) directing it to the secretory pathway and a conserved C-terminal BURP domain (residues 384-595) containing the characteristic cysteine-histidine (CH) motif pattern. The intervening variable region contains repeated sequence units. PG1beta-like BURP proteins in rice, such as the well-characterized OsBURP16 and OsBURP14, function as non-catalytic beta-subunits of polygalacturonase isozyme 1, modulating cell wall pectin remodeling. OsBURP16 overexpression increases polygalacturonase activity, decreases pectin content, and reduces cell adhesion. These proteins are regulated by the ethylene signaling transcription factor OsEIL2 and are strongly induced by ABA, ethylene, salt stress, and drought. B8BAB0 has not been directly characterized experimentally (UniProt protein evidence level 4, Predicted), and its specific biological role remains to be determined.
Q: Which BURP subfamily does B8BAB0 belong to based on phylogenetic analysis within the 17 rice BURP genes, and does it cluster with OsBURP12/OsBURP16 or with a different PG1beta-like clade?
Q: Is B8BAB0 expressed under specific stress conditions (drought, salt, ABA treatment) or developmental stages, similar to characterized PG1beta-like BURP proteins in rice?
Q: Does B8BAB0 physically interact with catalytic polygalacturonase subunits, and does it affect PG enzyme activity when co-expressed?
Experiment: Generate transgenic rice lines overexpressing B8BAB0 and measure polygalacturonase activity, pectin content, and cell adhesion in leaf tissue. Compare phenotypes under normal and salt/drought stress conditions to determine if B8BAB0 modulates stress tolerance via cell wall remodeling.
Hypothesis: B8BAB0 functions as a non-catalytic beta-subunit of polygalacturonase and its overexpression increases PG activity and decreases cell wall pectin content, similar to OsBURP16.
Type: transgenic overexpression / functional assay
Experiment: Express B8BAB0 fused to a fluorescent reporter (e.g. GFP) in rice protoplasts or stable transformants and determine subcellular localization by confocal microscopy, with co-localization analysis using cell wall markers.
Hypothesis: B8BAB0 is secreted to the apoplast or cell wall via its signal peptide and colocalizes with polygalacturonase enzymes.
Type: subcellular localization
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The protein B8BAB0 (ORF: OsI_29064) is a confirmed BURP domain-containing protein from rice (Oryza sativa subsp. indica) (ren2023genomewideidentificationand pages 1-2). The BURP protein family is a plant-specific group named after four founding members: BNM2 (microsporogenesis-specific protein), USP (unknown seed protein), RD22 (responsive to dehydration 22 protein), and PG1β (non-catalytic β-subunit of polygalacturonase isozyme 1) (ren2023genomewideidentificationand pages 1-2). Rice contains 17 BURP family genes classified into seven subfamilies: BNM2-like, USP-like, RD22-like, PG1β-like, BURP V, BURP VI, and BURP VII (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, ren2023genomewideidentificationand pages 4-6).
BURP domain-containing proteins share a characteristic structural organization consisting of three main components (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4):
N-terminal signal peptide: A hydrophobic region of approximately 20 amino acids that directs proteins to the secretory pathway. However, not all BURP family members possess this signal peptide (ren2023genomewideidentificationand pages 4-6).
Variable region: Located between the signal peptide and BURP domain, this region contains either a short conserved sequence or repeat sequence units. This variable region is a major source of functional diversification within the family (ren2023genomewideidentificationand pages 1-2). The RD22 subfamily is distinguished by having approximately 20 amino acid repeats in this region, while BNM2 proteins lack this repeat-containing segment (ren2023genomewideidentificationand pages 1-2).
Conserved C-terminal BURP domain: Comprising approximately 230 amino acids, this domain defines the family and contains the signature cysteine-histidine (CH) motif pattern: CH-X10-CH-X25-27-CH-X25-26-CH-X8-W, where X represents any amino acid residue (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6). The BURP domain also features two conserved phenylalanines (FF) at its N-terminal side and highly conserved valine (V), aspartic acid (D), threonine (T), proline (P), and glycine (G) residues at the C-terminal portion (ren2023genomewideidentificationand pages 1-2).
The PG1β-like subfamily possesses an additional distinguishing feature: a 14-amino-acid region containing the sequence FTNYGXXGNGGXXX (where X can be any amino acid residue) (ren2023genomewideidentificationand pages 1-2).
| Feature category | Component / subfamily | Structural characteristics | Distinguishing notes / likely functional implication | Evidence |
|---|---|---|---|---|
| Core domain architecture | N-terminal signal peptide | Typically an N-terminal hydrophobic signal peptide of about 20 amino acids; many BURP proteins are predicted to enter the secretory pathway, though some family members lack a clear signal peptide | Supports secretion or targeting to extracellular/periplasmic, vacuolar, or endomembrane compartments; consistent with roles in cell wall, apoplast, or storage-associated processes | (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4, ren2023genomewideidentificationand pages 4-6) |
| Core domain architecture | Variable internal region | Between the signal peptide and BURP domain lies a short conserved region and/or a variable segment often containing repeated sequence units; this region differs markedly among subfamilies | Major source of family diversification; repeat content is especially characteristic of some RD22-like members, while BNM2 proteins may lack the repeat segment | (ren2023genomewideidentificationand pages 1-2) |
| Core domain architecture | C-terminal BURP domain | Conserved C-terminal BURP domain of about 230 amino acids | Defines the family; strong C-terminal conservation contrasts with highly variable N-terminal/intervening regions | (ren2023genomewideidentificationand pages 1-2) |
| Conserved motif | Canonical BURP CH motif | Conserved cysteine/histidine-rich BURP-domain signature: CH-X10-CH-X25-27-CH-X25-26-CH-X8-W | This motif is a major diagnostic feature of BURP proteins and is widely used in family identification/classification | (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6) |
| Conserved residues | N- and C-terminal BURP-domain features | Two conserved phenylalanines (FF) near the N-terminal side of the BURP structural region; highly conserved V, D, T, P, G residues toward the C-terminal portion of the BURP domain | Indicates strong structural conservation within the BURP domain despite wide divergence elsewhere in the proteins | (ren2023genomewideidentificationand pages 1-2) |
| Structural comparison note | PG catalytic motifs vs BURP motifs | The motifs NTD, DD, GHG, and RIK are hallmark catalytic-site features of polygalacturonases (PGs), not of the BURP domain itself | Relevant chiefly for interpreting PG1β-like BURP proteins as polygalacturonase-associated proteins; these motifs define catalytic PG enzymes rather than the BURP scaffold | (safran2023plantpolygalacturonasestructures pages 1-4) |
| Subfamily classification | BNM2-like | Often lacks the repeat-containing variable segment seen in some other BURP proteins; part of the original defining BURP set | Associated with pollen grain embryogenesis / reproductive development in plants | (ren2023genomewideidentificationand pages 1-2) |
| Subfamily classification | USP-like | BURP proteins related to unknown seed proteins; generally secretory-pathway-associated proteins with conserved C-terminal BURP domain | Frequently linked to seed development and storage-related compartments | (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4) |
| Subfamily classification | RD22-like | Distinguished by a variable region that may contain repeated units; only RD22 proteins were noted to have ~20-amino-acid repeats between the signal peptide and BURP domain | Often ABA- and drought-responsive; commonly implicated in abiotic-stress biology | (ren2023genomewideidentificationand pages 1-2) |
| Subfamily classification | PG1β-like | Characterized by a distinctive 14-amino-acid region containing FTNYGXXGNGGXXX; includes rice OsBURP14/OsBURP16-type proteins | Associated with the β-subunit of polygalacturonase isozyme 1 and thus with pectin/cell-wall remodeling rather than independent glycosidase catalysis | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10) |
| Subfamily classification | BURP V | Rice BURP-family clade identified in genome-wide classification; structurally within the BURP superfamily but less functionally characterized in the cited sources | Likely lineage-expanded monocot/rice-associated BURP branch; specific biochemical role remains unclear from available evidence | (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, ren2023genomewideidentificationand pages 4-6) |
| Subfamily classification | BURP VI | Rice-enriched/monocot-dominated BURP clade identified by phylogenetic analysis | Suggests diversification of BURP functions in monocots, but direct biochemical features are not detailed in the cited sources | (ren2023genomewideidentificationand pages 4-6) |
| Subfamily classification | BURP VII | Rice-enriched/monocot-dominated BURP clade identified by phylogenetic analysis | As with BURP VI, indicates lineage-specific expansion; precise structural distinctions beyond phylogenetic placement are not resolved here | (ren2023genomewideidentificationand pages 4-6) |
| Family-level functional interpretation | Secreted structural/regulatory proteins | Many BURP proteins are not catalytic enzymes themselves; instead they are implicated in extracellular or endomembrane processes such as stress adaptation, seed development, or modulation of PG activity/cell-wall properties | Important for annotation of poorly characterized rice BURP proteins such as B8BAB0: function is often inferred from subfamily/domain context rather than direct enzymology | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10) |
Table: This table summarizes the conserved architecture, signature motifs, and major subfamilies of plant BURP-domain proteins, highlighting which features are universal and which are subfamily-specific. It is useful for inferring the likely properties of poorly characterized rice BURP proteins such as B8BAB0.
BURP domain-containing proteins are not catalytic enzymes themselves but rather function as structural or regulatory proteins in extracellular and endomembrane processes (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4). The functional role of B8BAB0 can be inferred from the well-characterized rice BURP proteins and the broader family characteristics.
The most extensively studied rice BURP proteins belong to the PG1β-like subfamily, particularly OsBURP16 and OsBURP14. These proteins function as non-catalytic β-subunits of polygalacturonase isozyme 1, playing a crucial role in cell wall pectin remodeling (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13).
Substrate and Mechanism: While BURP proteins themselves do not possess catalytic activity, they are associated with polygalacturonase (PG) enzymes that hydrolyze α-(1-4) glycosidic bonds between adjacent non-methylesterified galacturonic acid (GalA) units in homogalacturonan (HG), the major pectic polysaccharide of plant cell walls (safran2023plantpolygalacturonasestructures pages 1-4). OsBURP16 overexpression in rice results in:
- Increased polygalacturonase enzyme activity
- Decreased pectin content in cell walls
- Reduced cell adhesion and cell wall integrity
- Enhanced sensitivity to abiotic stresses (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13)
Different BURP subfamilies have distinct specialized roles (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4):
| Subfamily / group | Representative proteins / examples | Primary function | Molecular mechanism / biochemical role | Biological processes regulated | Typical subcellular localization | Evidence |
|---|---|---|---|---|---|---|
| PG1β-like BURP proteins | Rice OsBURP16, OsBURP14; tomato PG1β referenced as archetype | Non-catalytic β-subunit of polygalacturonase isozyme 1; promotes cell-wall pectin remodeling rather than acting as an independent glycosidase | OsBURP16 is associated with increased polygalacturonase (PG) activity, reduced pectin content, reduced cell adhesion, and altered cell-wall integrity; this links BURP proteins to pectin degradation pathways in the wall/apoplast (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, safran2023plantpolygalacturonasestructures pages 1-4) | Abiotic stress sensitivity, cell adhesion, leaf senescence-associated wall remodeling, developmental wall changes (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, safran2023plantpolygalacturonasestructures pages 1-4) | Secretory pathway/extracellular compartment; many BURP proteins carry N-terminal signal peptides and are predicted to localize to periplasmic or extracellular space, consistent with wall-associated function (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6) | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, safran2023plantpolygalacturonasestructures pages 1-4, ren2023genomewideidentificationand pages 4-6) |
| PG1β-like BURP proteins in rice | OsBURP16 | Demonstrated negative regulator of rice tolerance to salt and drought stress | Strongly induced by ABA, ACC, NaCl, PEG, and darkness; overexpression decreases pectin content and increases PG activity, linking hormone/stress signaling to cell-wall remodeling (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13) | Salt stress response, drought response, water-loss control, dark-induced senescence (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13) | Likely extracellular/apoplastic or wall-associated through secretion, inferred from BURP family architecture and PG1β-like role (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6) | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, ren2023genomewideidentificationand pages 4-6) |
| PG1β-like BURP proteins in rice | OsBURP14 | Closely related PG1β-like BURP protein functioning with OsBURP16 downstream of ethylene signaling | OsEIL2 binds the OsBURP14 promoter at EIN3-binding-site-like motifs, indicating transcriptional control in a stress-response pathway; functional inference supports a role in pectin/cell-wall regulation (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10) | Abiotic stress response and likely cell-wall remodeling under ethylene/stress signaling (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13) | Likely secreted/extracellular, by family architecture inference (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6) | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, ren2023genomewideidentificationand pages 4-6) |
| RD22-like BURP proteins | RD22-type BURP proteins in Arabidopsis and other plants; apple MdRD genes as recent comparative examples | Stress-responsive BURP proteins, especially associated with ABA and drought/dehydration signaling | Induced by ABA or drought; some members are reported to enhance tolerance and may influence cell-wall or extracellular stress adaptation rather than catalyzing a defined reaction themselves (ren2023genomewideidentificationand pages 1-2) | Drought response, salinity response, broader abiotic stress adaptation (ren2023genomewideidentificationand pages 1-2) | Often secreted/periplasmic or extracellular; some BURP proteins in stress-related clades have been described as apoplastic in other plant studies, and recent genome-wide analyses predict many BURP proteins in extracellular/periplasmic space (ren2023genomewideidentificationand pages 2-4, ren2023genomewideidentificationand pages 4-6) | (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4, ren2023genomewideidentificationand pages 4-6) |
| USP-like BURP proteins | Broad bean VfUSP, Arabidopsis AtUSPL1, apple MdUSP1-3 | Seed-associated BURP proteins involved in seed development and storage-related processes | Non-storage proteins expressed during seed development; overexpression of AtUSPL1 distorts seed development, supporting a developmental/structural role rather than enzyme catalysis (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4) | Seed development, protein storage-associated development, possibly seed maturation programs (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4) | Protein storage vacuoles, provacuolar compartments, secretory pathway-derived vesicles (ren2023genomewideidentificationand pages 2-4) | (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4) |
| BNM2-like BURP proteins | BNM2 from Brassica; BURP-family reproductive proteins | Reproductive/developmental BURP proteins linked to pollen grain embryogenesis or early seed-associated differentiation | Distinguished structurally by BURP architecture with less repeat-rich variable region; developmental function inferred from highly specific reproductive expression (ren2023genomewideidentificationand pages 1-2) | Pollen embryogenesis, reproductive development (ren2023genomewideidentificationand pages 1-2) | Golgi apparatus, provacuole region, protein storage vesicles in reported family members (ren2023genomewideidentificationand pages 2-4) | (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4) |
| Rice BURP protein involved in male reproduction | OsRAFTIN1 (reported BURP-containing protein in rice) | Anther/chorion-associated BURP protein required for normal male reproductive development | Specifically expressed in rice anthers/chorion during rapid post-meiotic microspore expansion, supporting a structural or secreted developmental role (ren2023genomewideidentificationand pages 2-4) | Anther development, pollen/male fertility processes (ren2023genomewideidentificationand pages 2-4) | Secretory/endomembrane or extracellular reproductive tissue compartment, inferred from BURP-family localization patterns (ren2023genomewideidentificationand pages 2-4) | (ren2023genomewideidentificationand pages 2-4) |
| BURP family as a whole | Rice BURP family; comparative analyses across apple, soybean, Arabidopsis, Medicago and other plants | Plant-specific family with conserved C-terminal BURP domain and variable N-terminal regions that support functional diversification | Family members commonly contain N-terminal signal peptides and a conserved BURP domain with CH-rich motif; functions converge on extracellular matrix, cell wall, stress response, and developmental regulation (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6) | Abiotic stress responses, cell-wall organization, seed development, senescence, reproductive development (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, ren2023genomewideidentificationand pages 2-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13) | Predominantly periplasmic/extracellular; some vacuolar or Golgi/provacuolar localizations depending on subfamily (ren2023genomewideidentificationand pages 2-4, ren2023genomewideidentificationand pages 4-6) | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, ren2023genomewideidentificationand pages 2-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, ren2023genomewideidentificationand pages 4-6) |
| Regulatory pathway connection in rice | OsEIL2 → OsBURP14 / OsBURP16 | Ethylene-signaling module linking transcriptional regulation to BURP-mediated wall remodeling | OsEIL2 directly binds promoters of OsBURP14 and OsBURP16 and activates their expression; increased BURP expression correlates with higher PG activity and lower pectin, providing a mechanistic chain from signaling to wall change (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13) | Ethylene/ABA-associated abiotic stress response, senescence, cell-wall-dependent stress sensitivity (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13) | OsEIL2 is nuclear, while downstream BURP proteins are inferred to function in the secretory/extracellular cell-wall compartment (jin2020ethyleneinsensitive3like2(oseil2) pages 4-7, jin2020ethyleneinsensitive3like2(oseil2) pages 13-16, ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6) | (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 4-7, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, ren2023genomewideidentificationand pages 4-6, jin2020ethyleneinsensitive3like2(oseil2) pages 13-16) |
Table: This table summarizes the major functional subfamilies of plant BURP-domain proteins, emphasizing rice examples such as OsBURP14 and OsBURP16. It links subfamily identity to molecular mechanism, biological process, and likely subcellular localization to support functional annotation.
BURP domain-containing proteins function primarily in extracellular compartments and secretory pathway-associated locations (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 2-4, ren2023genomewideidentificationand pages 4-6):
Periplasmic/extracellular space: The predominant localization for most BURP proteins, consistent with their N-terminal signal peptides and roles in cell wall modification. Predictions indicate that BURP proteins are predominantly localized to the periplasmic space and extracellular regions (ren2023genomewideidentificationand pages 4-6).
Protein storage vacuoles: USP-like proteins (e.g., Arabidopsis AtUSPL1 and broad bean VfUSP) localize to protein storage vacuoles, where they function during seed development (ren2023genomewideidentificationand pages 2-4).
Golgi apparatus and provacuole regions: BNM2-like subfamily proteins have been observed in Golgi and provacuolar compartments, consistent with their developmental roles (ren2023genomewideidentificationand pages 2-4).
Apoplast: Some RD22-like proteins function in the apoplastic space, particularly those involved in stress responses (ren2023genomewideidentificationand pages 2-4).
The signal peptide is cleaved during protein processing as proteins transit through the secretory pathway, allowing mature BURP proteins to function in the cell wall and extracellular matrix (ren2023genomewideidentificationand pages 1-2, ren2023genomewideidentificationand pages 4-6).
BURP domain proteins participate in several specific signaling and biochemical pathways rather than having broad pleiotropic effects:
The most precisely defined pathway involves the ethylene signaling transcription factor OsEIL2 (ETHYLENE INSENSITIVE 3-LIKE 2), which directly regulates OsBURP14 and OsBURP16 expression (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13). Mechanistically:
OsEIL2 is a nuclear-localized transcription factor that accumulates in the nucleus upon ethylene treatment or proteasome inhibition (jin2020ethyleneinsensitive3like2(oseil2) pages 4-7, jin2020ethyleneinsensitive3like2(oseil2) pages 13-16). The OsEIL2-BURP regulatory module links hormone signaling to cell wall remodeling during stress responses (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13).
BURP genes, particularly RD22-like and PG1β-like members, are strongly induced by abscisic acid (ABA) treatment (ren2023genomewideidentificationand pages 1-2, jin2020ethyleneinsensitive3like2(oseil2) pages 7-10). OsBURP16 expression is induced up to 40-fold by ABA, 400-fold by the ethylene precursor ACC, 150-fold by NaCl, and 600-fold by polyethylene glycol (PEG) treatment (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10). The protein is also dramatically upregulated by darkness (270-fold after 24 hours), linking it to senescence-associated processes (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10).
BURP proteins, particularly the PG1β-like subfamily, function in the pectin degradation pathway by modulating polygalacturonase enzyme activity (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13, safran2023plantpolygalacturonasestructures pages 1-4). This pathway involves:
- Hydrolysis of α-(1-4) glycosidic bonds in homogalacturonan
- Reduction in cell wall pectin content
- Altered cell wall mechanical properties and cell adhesion
- Production of oligogalacturonides (OGs) that may serve as signaling molecules (safran2023plantpolygalacturonasestructures pages 1-4)
Transgenic rice plants overexpressing OsBURP16 show enhanced PG activity, reduced pectin content, decreased cell adhesion, and increased sensitivity to salt and drought stress (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13). Conversely, reduced OsBURP expression results in decreased PG activity, increased pectin content, and enhanced stress tolerance (jin2020ethyleneinsensitive3like2(oseil2) pages 10-13).
BURP proteins integrate multiple stress signals through their regulation by both ethylene and ABA pathways. This integration affects:
- Cellular water loss rates during dehydration
- H₂O₂ accumulation under stress conditions
- Dark-induced leaf senescence
- Plant survival under salt and drought conditions (jin2020ethyleneinsensitive3like2(oseil2) pages 7-10, jin2020ethyleneinsensitive3like2(oseil2) pages 10-13)
Recent genome-wide analyses have expanded our understanding of BURP protein diversity and evolution (ren2023genomewideidentificationand pages 1-2). A 2023 study identified 18 BURP domain-containing genes in apple (Malus domestica), demonstrating that expression patterns differ significantly among family members under various stress conditions, with specific genes showing upregulation under NaCl and PEG treatments (ren2023genomewideidentificationand pages 1-2).
Single-cell transcriptomics studies in rice have identified OsBURP genes among those involved in photosynthesis and gravitropic responses in plumules, highlighting their developmental roles beyond stress response (hu2024harnessingsinglecelland pages 1-2). This approach has revealed cell-type-specific expression patterns that were previously masked in bulk tissue analyses (hu2024harnessingsinglecelland pages 1-2).
Recent structural biology work on plant polygalacturonases has elucidated how PG enzymes fine-tune pectin structure through differences in enzyme processivity, providing context for understanding how BURP-associated PG activity modulates cell wall properties (safran2023plantpolygalacturonasestructures pages 1-4). These structural studies have shown that different PG isozymes produce oligogalacturonides of varying sizes, which may have distinct signaling functions (safran2023plantpolygalacturonasestructures pages 1-4).
The BURP domain protein family represents a plant-specific innovation for regulating extracellular processes, particularly cell wall dynamics and stress adaptation. The family's structural conservation at the C-terminal BURP domain combined with N-terminal diversification has enabled functional specialization across subfamilies while maintaining core structural integrity (ren2023genomewideidentificationand pages 1-2).
For B8BAB0 specifically, while direct functional studies are not available in the literature, its classification as a BURP domain-containing protein allows inference of several key properties based on family-wide characteristics:
The evolutionary retention of 17 BURP genes in rice indicates functional importance and likely subfunctionalization, with different family members responding to distinct developmental or environmental cues (jin2020ethyleneinsensitive3like2(oseil2) pages 1-4). This diversification allows fine-tuned control of cell wall properties across different tissues, developmental stages, and stress conditions.
B8BAB0 is a member of the plant-specific BURP domain protein family in rice, characterized by a conserved C-terminal BURP domain containing the signature CH-rich motif. While specific functional data for this particular protein are limited, extensive research on related rice BURP proteins, particularly OsBURP14 and OsBURP16, provides a framework for understanding its likely biological role. BURP proteins function primarily as secreted structural or regulatory proteins in the extracellular matrix and cell wall, where they modulate processes including pectin metabolism, abiotic stress responses, and developmental transitions. The proteins are integrated into ethylene and ABA signaling pathways, providing a molecular link between hormone perception and cell wall remodeling. Future functional characterization of B8BAB0 would benefit from examining its expression patterns under various stress conditions, determining its precise subcellular localization, and identifying physical or genetic interactions with other cell wall-related proteins.
Primary Literature (2020-2024):
- Jin et al. (2020), Plant Science 292:110353 - Detailed functional analysis of OsBURP16 in ethylene signaling and stress response
- Ren et al. (2023), Physiology and Molecular Biology of Plants 29(11):1717-1731 - Genome-wide BURP family identification and characterization
- Hu et al. (2024), Plants 13(24):3476 - Single-cell transcriptomics applications identifying OsBURP in developmental processes
- Safran et al. (2023), The Plant Cell 35(8):3073-3091 - Structural analysis of polygalacturonases and pectin dynamics
Databases and Resources:
- UniProt: B8BAB0
- Pfam: PF03181 (BURP domain)
- InterPro: IPR004873 (BURP_dom), IPR051897 (PG-associated_BURP)
References
(ren2023genomewideidentificationand pages 1-2): Jiaxuan Ren, Li Feng, Lili Guo, Huimin Gou, Shixiong Lu, and Juan Mao. Genome-wide identification and expression analysis of the burp domain-containing genes in malus domestica. Physiology and Molecular Biology of Plants, 29:1717-1731, Nov 2023. URL: https://doi.org/10.1007/s12298-023-01393-7, doi:10.1007/s12298-023-01393-7. This article has 4 citations and is from a peer-reviewed journal.
(jin2020ethyleneinsensitive3like2(oseil2) pages 1-4): Jing Jin, Jianli Duan, Chi Shan, Zhiling Mei, Haiying Chen, Huafeng Feng, Jian Zhu, and Weiming Cai. Ethylene insensitive3-like2 (oseil2) confers stress sensitivity by regulating osburp16, the β subunit of polygalacturonase (pg1β-like) subfamily gene in rice. Plant science : an international journal of experimental plant biology, 292:110353, Mar 2020. URL: https://doi.org/10.1016/j.plantsci.2019.110353, doi:10.1016/j.plantsci.2019.110353. This article has 43 citations.
(ren2023genomewideidentificationand pages 4-6): Jiaxuan Ren, Li Feng, Lili Guo, Huimin Gou, Shixiong Lu, and Juan Mao. Genome-wide identification and expression analysis of the burp domain-containing genes in malus domestica. Physiology and Molecular Biology of Plants, 29:1717-1731, Nov 2023. URL: https://doi.org/10.1007/s12298-023-01393-7, doi:10.1007/s12298-023-01393-7. This article has 4 citations and is from a peer-reviewed journal.
(ren2023genomewideidentificationand pages 2-4): Jiaxuan Ren, Li Feng, Lili Guo, Huimin Gou, Shixiong Lu, and Juan Mao. Genome-wide identification and expression analysis of the burp domain-containing genes in malus domestica. Physiology and Molecular Biology of Plants, 29:1717-1731, Nov 2023. URL: https://doi.org/10.1007/s12298-023-01393-7, doi:10.1007/s12298-023-01393-7. This article has 4 citations and is from a peer-reviewed journal.
(safran2023plantpolygalacturonasestructures pages 1-4): Josip Safran, Wafae Tabi, Vanessa Ung, Adrien Lemaire, Olivier Habrylo, Julie Bouckaert, Maxime Rouffle, Aline Voxeur, Paula Pongrac, Solène Bassard, Roland Molinié, Jean-Xavier Fontaine, Serge Pilard, Corinne Pau-Roblot, Estelle Bonnin, Danaé Sonja Larsen, Mélanie Morel-Rouhier, Jean-Michel Girardet, Valérie Lefebvre, Fabien Sénéchal, Davide Mercadante, and Jérôme Pelloux. Plant polygalacturonase structures specify enzyme dynamics and processivities to fine-tune cell wall pectins. The Plant cell, 35:3073-3091, May 2023. URL: https://doi.org/10.1093/plcell/koad134, doi:10.1093/plcell/koad134. This article has 48 citations.
(jin2020ethyleneinsensitive3like2(oseil2) pages 7-10): Jing Jin, Jianli Duan, Chi Shan, Zhiling Mei, Haiying Chen, Huafeng Feng, Jian Zhu, and Weiming Cai. Ethylene insensitive3-like2 (oseil2) confers stress sensitivity by regulating osburp16, the β subunit of polygalacturonase (pg1β-like) subfamily gene in rice. Plant science : an international journal of experimental plant biology, 292:110353, Mar 2020. URL: https://doi.org/10.1016/j.plantsci.2019.110353, doi:10.1016/j.plantsci.2019.110353. This article has 43 citations.
(jin2020ethyleneinsensitive3like2(oseil2) pages 10-13): Jing Jin, Jianli Duan, Chi Shan, Zhiling Mei, Haiying Chen, Huafeng Feng, Jian Zhu, and Weiming Cai. Ethylene insensitive3-like2 (oseil2) confers stress sensitivity by regulating osburp16, the β subunit of polygalacturonase (pg1β-like) subfamily gene in rice. Plant science : an international journal of experimental plant biology, 292:110353, Mar 2020. URL: https://doi.org/10.1016/j.plantsci.2019.110353, doi:10.1016/j.plantsci.2019.110353. This article has 43 citations.
(jin2020ethyleneinsensitive3like2(oseil2) pages 4-7): Jing Jin, Jianli Duan, Chi Shan, Zhiling Mei, Haiying Chen, Huafeng Feng, Jian Zhu, and Weiming Cai. Ethylene insensitive3-like2 (oseil2) confers stress sensitivity by regulating osburp16, the β subunit of polygalacturonase (pg1β-like) subfamily gene in rice. Plant science : an international journal of experimental plant biology, 292:110353, Mar 2020. URL: https://doi.org/10.1016/j.plantsci.2019.110353, doi:10.1016/j.plantsci.2019.110353. This article has 43 citations.
(jin2020ethyleneinsensitive3like2(oseil2) pages 13-16): Jing Jin, Jianli Duan, Chi Shan, Zhiling Mei, Haiying Chen, Huafeng Feng, Jian Zhu, and Weiming Cai. Ethylene insensitive3-like2 (oseil2) confers stress sensitivity by regulating osburp16, the β subunit of polygalacturonase (pg1β-like) subfamily gene in rice. Plant science : an international journal of experimental plant biology, 292:110353, Mar 2020. URL: https://doi.org/10.1016/j.plantsci.2019.110353, doi:10.1016/j.plantsci.2019.110353. This article has 43 citations.
(hu2024harnessingsinglecelland pages 1-2): Yuzhao Hu, Linkan Dash, Gregory May, Nagesh Sardesai, and Stéphane Deschamps. Harnessing single-cell and spatial transcriptomics for crop improvement. Plants, 13:3476, Dec 2024. URL: https://doi.org/10.3390/plants13243476, doi:10.3390/plants13243476. This article has 11 citations.
id: B8BAB0
gene_symbol: B8BAB0
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:39946
label: Oryza sativa subsp. indica
description: >-
B8BAB0 (ORF OsI_29064) is a BURP domain-containing protein from rice (Oryza sativa
subsp. indica). It belongs to the PG1beta-like subfamily of BURP proteins, classified
by PANTHER (PTHR31458:SF2, Polygalacturonase 1 beta-like protein 2) and containing the
InterPro PG-associated BURP domain (IPR051897). The protein is 623 amino acids long,
with an N-terminal signal peptide (residues 1-21) directing it to the secretory pathway
and a conserved C-terminal BURP domain (residues 384-595) containing the characteristic
cysteine-histidine (CH) motif pattern. The intervening variable region contains
repeated sequence units. PG1beta-like BURP proteins in rice, such as the well-characterized
OsBURP16 and OsBURP14, function as non-catalytic beta-subunits of polygalacturonase
isozyme 1, modulating cell wall pectin remodeling. OsBURP16 overexpression increases
polygalacturonase activity, decreases pectin content, and reduces cell adhesion. These
proteins are regulated by the ethylene signaling transcription factor OsEIL2 and are
strongly induced by ABA, ethylene, salt stress, and drought. B8BAB0 has not been directly
characterized experimentally (UniProt protein evidence level 4, Predicted), and its
specific biological role remains to be determined.
existing_annotations: []
references:
- id: file:ORYSI/B8BAB0/B8BAB0-uniprot.txt
title: UniProtKB TrEMBL entry for B8BAB0, BURP domain-containing protein
findings:
- statement: >-
B8BAB0 is an unreviewed 623 aa protein with a signal peptide (aa 1-21) and
BURP domain (aa 384-595), classified into PANTHER family PTHR31458 (Polygalacturonase
1 beta-like protein 2).
- id: file:ORYSI/B8BAB0/B8BAB0-deep-research-falcon.md
title: Falcon deep research report on B8BAB0 BURP domain-containing protein
findings:
- statement: >-
BURP domain proteins are plant-specific, non-catalytic proteins functioning in
extracellular and endomembrane processes. The PG1beta-like subfamily members
OsBURP16 and OsBURP14 modulate polygalacturonase activity and cell wall pectin
content in rice.
- statement: >-
OsBURP16 expression is strongly induced by ABA (40-fold), ACC (400-fold), NaCl
(150-fold), PEG (600-fold), and darkness (270-fold), and is regulated by the
ethylene signaling transcription factor OsEIL2.
- id: file:interpro/panther/PTHR31458/PTHR31458-metadata.yaml
title: PANTHER family PTHR31458 metadata - Polygalacturonase-associated BURP domain-containing protein
findings:
- statement: >-
PTHR31458 encompasses 1738 proteins across 1244 taxa and 13 subfamilies,
including non-catalytic subunits of polygalacturonase and BURP domain proteins
involved in plant cell size and growth regulation.
core_functions:
- description: >-
Predicted non-catalytic regulatory subunit of polygalacturonase, inferred from
PG1beta-like BURP subfamily membership (PTHR31458:SF2). Related rice proteins
OsBURP16 and OsBURP14 modulate polygalacturonase enzymatic activity and cell wall
pectin content. Contains an N-terminal signal peptide consistent with secretion
to the extracellular matrix.
molecular_function:
id: GO:0030234
label: enzyme regulator activity
directly_involved_in:
- id: GO:0071555
label: cell wall organization
locations:
- id: GO:0009505
label: plant-type cell wall
- id: GO:0048046
label: apoplast
supported_by:
- reference_id: file:ORYSI/B8BAB0/B8BAB0-uniprot.txt
supporting_text: >-
PANTHER classification PTHR31458:SF2 POLYGALACTURONASE 1 BETA-LIKE PROTEIN 2
and InterPro IPR051897 PG-associated BURP domain.
- reference_id: file:ORYSI/B8BAB0/B8BAB0-deep-research-falcon.md
supporting_text: >-
OsBURP16 overexpression in rice results in increased polygalacturonase enzyme
activity, decreased pectin content in cell walls, reduced cell adhesion and
cell wall integrity.
- reference_id: file:interpro/panther/PTHR31458/PTHR31458-metadata.yaml
supporting_text: >-
This family of proteins includes non-catalytic subunits of polygalacturonase
as well as proteins containing a BURP domain at the C-terminus.
proposed_new_terms: []
suggested_questions:
- question: >-
Which BURP subfamily does B8BAB0 belong to based on phylogenetic analysis
within the 17 rice BURP genes, and does it cluster with OsBURP12/OsBURP16 or
with a different PG1beta-like clade?
- question: >-
Is B8BAB0 expressed under specific stress conditions (drought, salt, ABA
treatment) or developmental stages, similar to characterized PG1beta-like
BURP proteins in rice?
- question: >-
Does B8BAB0 physically interact with catalytic polygalacturonase subunits,
and does it affect PG enzyme activity when co-expressed?
suggested_experiments:
- hypothesis: >-
B8BAB0 functions as a non-catalytic beta-subunit of polygalacturonase and its
overexpression increases PG activity and decreases cell wall pectin content,
similar to OsBURP16.
description: >-
Generate transgenic rice lines overexpressing B8BAB0 and measure
polygalacturonase activity, pectin content, and cell adhesion in leaf tissue.
Compare phenotypes under normal and salt/drought stress conditions to determine
if B8BAB0 modulates stress tolerance via cell wall remodeling.
experiment_type: transgenic overexpression / functional assay
- hypothesis: >-
B8BAB0 is secreted to the apoplast or cell wall via its signal peptide and
colocalizes with polygalacturonase enzymes.
description: >-
Express B8BAB0 fused to a fluorescent reporter (e.g. GFP) in rice protoplasts
or stable transformants and determine subcellular localization by confocal
microscopy, with co-localization analysis using cell wall markers.
experiment_type: subcellular localization