Casparian strip membrane protein 2 (PtCASP2) is a small tetraspan (four-transmembrane, MARVEL-domain) plasma-membrane protein of the Populus CASP family. It is not an enzyme; instead it acts as a membrane scaffold that demarcates the Casparian strip membrane domain (CSD) in the root endodermis. By concentrating into a sharply delimited belt-shaped microdomain of the plasma membrane, CASP2 organizes membrane-cell wall junctions and recruits the lignin-polymerizing machinery that builds the Casparian strip, a localized lignified cell wall modification that forms the apoplastic diffusion barrier of the endodermis. The protein is N-glycosylated and forms homodimers and heterodimers with other CASP family members within this microdomain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005886 plasma membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Plasma membrane localization is the well-supported cellular location for this CASP-family tetraspan protein, which forms a restricted belt-shaped microdomain in the root endodermal plasma membrane. Reason: The UniProt entry documents a multi-pass cell membrane localization with a belt-shaped distribution coinciding with the Casparian strip membrane domain, consistent with the conserved CASP family. Plasma membrane is the correct and core cellular-component annotation. Supporting Evidence: file:POPTR/CASP2/CASP2-uniprot.txt SUBCELLULAR LOCATION: Cell membrane file:POPTR/CASP2/CASP2-uniprot.txt DR GO; GO:0005886; C:plasma membrane; IBA:GO_Central. |
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Download this section (compressed HTML)Q: Is PtCASP2 expressed specifically in the root endodermis and does it localize to a belt-shaped Casparian strip domain in Populus as it does in Arabidopsis?
Q: Do CASP2 and the closely linked CASP3 (both on chromosome 16) act redundantly in poplar Casparian strip formation?
Experiment: Express a fluorescently tagged PtCASP2 in poplar roots and image its subcellular distribution relative to lignin deposition to confirm Casparian strip domain localization.
Type: fluorescence localization
Experiment: Generate CASP loss-of-function or RNAi lines in Populus and assess Casparian strip integrity and apoplastic barrier function using tracer (e.g. propidium iodide) penetration assays.
Type: targeted functional assay
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