Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
A novel protein family mediates Casparian strip formation in the endodermis.
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CASPs (Casparian strip membrane domain proteins) are transmembrane proteins that mark a plasma-membrane domain predicting Casparian strip formation; CASP1 forms complexes with other CASPs, becomes immobile upon localization, and sediments as a large polymer — the hallmarks of a membrane scaffold.
"These 'CASPs' (Casparian strip membrane domain proteins) specifically mark a membrane domain that predicts the formation of Casparian strips. CASP1 displays numerous features required for a constituent of a plant junctional complex: it forms complexes with other CASPs; it becomes immobile upon localization; and it sediments like a large polymer."
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CASP double mutants display disorganized Casparian strips, showing CASPs structure and localize this cell wall modification.
"CASP double mutants display disorganized Casparian strips, demonstrating a role for CASPs in structuring and localizing this cell wall modification."
Functional and Evolutionary Analysis of the CASPARIAN STRIP MEMBRANE DOMAIN PROTEIN Family.
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CASPs are four-membrane-span proteins that mediate deposition of Casparian strips in the endodermis by recruiting the lignin polymerization machinery; the CASP membrane domain has all the hallmarks of a membrane scaffold.
"CASPARIAN STRIP MEMBRANE DOMAIN PROTEINS (CASPs) are four-membrane-span proteins that mediate the deposition of Casparian strips in the endodermis by recruiting the lignin polymerization machinery. CASPs show high stability in their membrane domain, which presents all the hallmarks of a membrane scaffold."
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The broader CASP-like family is found across all land plants and green algae; non-plant homologs are MARVEL-family proteins. This is the family/ nomenclature reference cited in the SbCASP1 UniProt entry.
"CASPLs were found in all major divisions of land plants as well as in green algae; homologs outside of the plant kingdom were identified as members of the MARVEL protein family."
Dirigent domain-containing protein is part of the machinery required for formation of the lignin-based Casparian strip in the root.
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The Casparian strip is composed of lignin polymerized by a NADPH oxidase and peroxidases; CASPs position this biosynthetic machinery by forming a plasma-membrane scaffold at the Casparian strip formation site.
"This junction is composed of lignin that is polymerized by oxidative coupling of monolignols through the action of a NADPH oxidase and peroxidases. Casparian strip domain proteins (CASPs) correctly position this biosynthetic machinery by forming a protein scaffold in the plasma membrane at the site where the Casparian strip forms."
The MYB36 transcription factor orchestrates Casparian strip formation.
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Localized CASPs recruit Peroxidase 64 (PER64), the NADPH oxidase RBOHF and the dirigent-like protein ESB1 to assemble the lignin polymerization machinery; the Casparian strip is a fine lignified band in the endodermal cell wall.
"Localized CASPs recruit Peroxidase 64 (PER64), a Respiratory Burst Oxidase Homolog F, and Enhanced Suberin 1 (ESB1), a dirigent-like protein, to assemble the lignin polymerization machinery."
The endodermis - development and differentiation of the plant's inner skin.
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The Casparian strip is the defining cell wall modification of the differentiated endodermis; CASPs localize precisely to a plasma-membrane domain underneath the Casparian strip, and the endodermis blocks apoplastic diffusion.
"The recent isolation of a novel protein family, the CASPs, that localizes precisely to a domain of the plasma membrane underneath the CS represents an excellent point of entry to explore CS function and formation."
Rice OsCASP1 orchestrates Casparian strip formation and suberin deposition in small lateral roots to maintain nutrient homeostasis.
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In rice (a grass, like sorghum), CASPs form a transmembrane scaffold to recruit lignin biosynthetic enzymes for Casparian strip formation; loss of OsCASP1 delays Casparian strip formation and causes uneven lignin deposition, disrupting nutrient homeostasis.
"Casparian strip membrane domain proteins (CASPs) form a transmembrane scaffold to recruit lignin biosynthetic enzymes for Casparian strip (CS) formation."
A new family of proteins is required for tethering of Casparian strip membrane domain and nutrient homoeostasis in rice.
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In rice, OsCASP1 is a core component of the Casparian strip-Casparian strip membrane domain (CS-CSD) junctional complex, forming a tight complex with GAPLESS proteins that tether the plasma membrane to the Casparian strip.
"The GAPLESS protein forms a tight complex with OsCASP1 in the plasma membrane, thereby mediating the CS-CSD junction."
Falcon deep-research report — Functional annotation of Sorghum bicolor CASP1 (UniProt C5YAP3; Sb06g033470)
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No primary publication directly assaying SbCASP1 (C5YAP3 / Sb06g033470) was retrieved; functional annotation rests on conserved CASP-family mechanism plus direct experimental evidence from closely related cereal CASP homologs (sorghum SbCASP4, sorghum SbCASP-LP1C1, rice OsCASP1) and Arabidopsis CASP research. SbCASP1 is most parsimoniously a CSD-localizing four-transmembrane scaffold protein, with function assigned by orthology.
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CASP-family proteins are four-transmembrane-span integral plasma-membrane proteins with cytosolic N- and C-termini that accumulate at the Casparian strip membrane domain (CSD), a specialized plasma-membrane region of root endodermal cells; sorghum SbCASP4 was experimentally localized to the plasma membrane and expressed in endodermal/Casparian-strip regions.
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The best-supported molecular role of CASP-family proteins is organizational rather than enzymatic — a stable membrane scaffold/fence that defines the CSD and recruits the lignin-polymerization machinery (RBOHF, ESB1, PER64, UCC1) to build the Casparian strip, a localized lignified cell wall modification of the endodermis.
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CASP-mediated barrier assembly is transcriptionally activated by MYB36 (which directly induces CASP1, ESB1, PER64) and is monitored by the CIF1/2-SGN3-SGN1 (SCHENGEN) surveillance pathway that triggers compensatory lignification/suberization when barrier defects are detected.
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Cereal CASP-family genes (sorghum SbCASP4, SbCASP-LP1C1; rice OsCASP1) provide direct experimental evidence that strengthening the root apoplastic barrier improves salt exclusion, ion homeostasis and selective mineral uptake, supporting the inferred role of SbCASP1 in the endodermal diffusion barrier and nutrient homeostasis.