CASP-like protein 1B1 (AtCASPL1B1, At5g44550) is a small tetraspan (four-transmembrane) plasma-membrane protein of the CASP-like (CASPL) subfamily of the MARVEL-related Casparian strip membrane domain protein family, belonging to the CASPL1 clade. It is expressed specifically in suberized endodermal cells of the root. CASPL1B1 physically interacts with the plasma-membrane aquaporin PIP2;1 and has been proposed to modulate aquaporin behaviour (e.g. via the phosphorylated form), consistent with a membrane scaffold/adaptor role organizing client proteins in the suberizing endodermis rather than an enzymatic or transport activity. It is transcriptionally up-regulated when the Casparian strip is defective (in myb36 mutants or after CIF2 peptide treatment) but is functionally redundant - simultaneous knockout of six endodermis-expressed CASPLs including CASPL1B1 in a quintuple-CASP (caspQ) background does not worsen the Casparian strip phenotype, and CASPL loss of function does not detectably alter whole-root hydraulic conductivity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Plasma membrane is the correct and well-supported localization for this multi-pass CASP-like protein. Reason: UniProt annotates CASPL1B1 as a multi-pass cell-membrane protein, the family is defined by plasma-membrane CASP/CASPL scaffolds (with direct IDA support for family members), and the deep-research synthesis places CASPL1B1 in the endodermal plasma membrane. Supporting Evidence: file:ARATH/CASPL1B1/CASPL1B1-uniprot.txt SUBCELLULAR LOCATION: Cell membrane file:ARATH/CASPL1B1/CASPL1B1-deep-research-falcon.md exclusively expressed in suberized endodermal cells |
| GO:0005515 protein binding | IPI PMID:21798944 Evidence for network evolution in an Arabidopsis interactome... | KEEP AS NON CORE | Summary: A real but uninformative high-throughput Y2H interaction (with NAC089); valid to retain but not a core function and not the biologically meaningful aquaporin interaction. Reason: The IPI comes from the large-scale Arabidopsis interactome map (binary Y2H) and the interactor is the transcription factor NAC089 (Q94F58); 'protein binding' is too generic to convey function, and this interaction is distinct from the experimentally characterized, functionally meaningful CASPL1B1-PIP2;1 aquaporin interaction reported elsewhere. Supporting Evidence: PMID:21798944 Evidence for network evolution in an Arabidopsis interactome map |
| GO:0005576 extracellular region | ISM GO_REF:0000122 | REMOVE | Summary: Incorrect localization for a four-transmembrane plasma-membrane protein; an automated sequence-model artifact. Reason: CASPL1B1 is a multi-pass (four-transmembrane) integral plasma-membrane protein, not a secreted/extracellular protein. The extracellular-region call is an automated sequence-model (ISM) inference that contradicts the UniProt topology and the entire CASP/CASPL family architecture, and should be removed. Supporting Evidence: file:ARATH/CASPL1B1/CASPL1B1-uniprot.txt SUBCELLULAR LOCATION: Cell membrane file:ARATH/CASPL1B1/CASPL1B1-uniprot.txt Multi-pass membrane |
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Download this section (compressed HTML)Q: Does the CASPL1B1-PIP2;1 interaction measurably regulate aquaporin gating or trafficking in the suberized endodermis, given the absence of a whole-root hydraulic phenotype?
Experiment: Cell-type-resolved hydraulic and water-channel assays (e.g. endodermal protoplast swelling, PIP2;1 phosphorylation status) in CASPL1B/1D higher-order mutants to detect local, non-bulk effects on aquaporin function.
Type: targeted physiology and biochemistry
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