| 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 (pqac-00000001, pqac-00000005, pqac-00000006, pqac-00000007) | Abiotic stress sensitivity, cell adhesion, leaf senescence-associated wall remodeling, developmental wall changes (pqac-00000001, pqac-00000005, pqac-00000006, pqac-00000007) | 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 (pqac-00000000, pqac-00000009) | (pqac-00000000, pqac-00000001, pqac-00000005, pqac-00000006, pqac-00000007, pqac-00000009) |
| 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 (pqac-00000005, pqac-00000006) | Salt stress response, drought response, water-loss control, dark-induced senescence (pqac-00000005, pqac-00000006) | Likely extracellular/apoplastic or wall-associated through secretion, inferred from BURP family architecture and PG1β-like role (pqac-00000000, pqac-00000009) | (pqac-00000000, pqac-00000005, pqac-00000006, pqac-00000009) |
| 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 (pqac-00000005) | Abiotic stress response and likely cell-wall remodeling under ethylene/stress signaling (pqac-00000005, pqac-00000006) | Likely secreted/extracellular, by family architecture inference (pqac-00000000, pqac-00000009) | (pqac-00000000, pqac-00000005, pqac-00000006, pqac-00000009) |
| 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 (pqac-00000000) | Drought response, salinity response, broader abiotic stress adaptation (pqac-00000000) | 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 (pqac-00000003, pqac-00000009) | (pqac-00000000, pqac-00000003, pqac-00000009) |
| 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 (pqac-00000000, pqac-00000003) | Seed development, protein storage-associated development, possibly seed maturation programs (pqac-00000000, pqac-00000003) | Protein storage vacuoles, provacuolar compartments, secretory pathway-derived vesicles (pqac-00000003) | (pqac-00000000, pqac-00000003) |
| 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 (pqac-00000000) | Pollen embryogenesis, reproductive development (pqac-00000000) | Golgi apparatus, provacuole region, protein storage vesicles in reported family members (pqac-00000003) | (pqac-00000000, pqac-00000003) |
| 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 (pqac-00000003) | Anther development, pollen/male fertility processes (pqac-00000003) | Secretory/endomembrane or extracellular reproductive tissue compartment, inferred from BURP-family localization patterns (pqac-00000003) | (pqac-00000003) |
| 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 (pqac-00000000, pqac-00000009) | Abiotic stress responses, cell-wall organization, seed development, senescence, reproductive development (pqac-00000000, pqac-00000001, pqac-00000003, pqac-00000005, pqac-00000006) | Predominantly periplasmic/extracellular; some vacuolar or Golgi/provacuolar localizations depending on subfamily (pqac-00000003, pqac-00000009) | (pqac-00000000, pqac-00000001, pqac-00000003, pqac-00000005, pqac-00000006, pqac-00000009) |
| 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 (pqac-00000001, pqac-00000005, pqac-00000006) | Ethylene/ABA-associated abiotic stress response, senescence, cell-wall-dependent stress sensitivity (pqac-00000001, pqac-00000005, pqac-00000006) | OsEIL2 is nuclear, while downstream BURP proteins are inferred to function in the secretory/extracellular cell-wall compartment (pqac-00000004, pqac-00000010, pqac-00000000, pqac-00000009) | (pqac-00000000, pqac-00000001, pqac-00000004, pqac-00000005, pqac-00000006, pqac-00000009, pqac-00000010) |


*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.*