CASP1

id: B9HBX2
gene_symbol: CASP1
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:3694
  label: Populus trichocarpa
description: Casparian strip membrane protein 1 (PtCASP1) 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, CASP1 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 forms homodimers and heterodimers with other CASP family members within this
  microdomain.
existing_annotations:
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: file:POPTR/CASP1/CASP1-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cell membrane'
    - reference_id: file:POPTR/CASP1/CASP1-uniprot.txt
      supporting_text: DR   GO; GO:0005886; C:plasma membrane; IBA:GO_Central.
references:
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings:
  - statement: GO_REF:0000120 supplied the plasma membrane GOA annotation reviewed in this file.
- id: file:POPTR/CASP1/CASP1-uniprot.txt
  title: UniProtKB reviewed entry for CASP1
  findings:
  - statement: UniProt identifies CASP1 as a CASP-family multi-pass cell membrane protein required for
      establishment of the Casparian strip membrane domain and formation of Casparian strips in the root endodermis.
- id: PMID:24920445
  title: Functional and evolutionary analysis of the CASPARIAN STRIP MEMBRANE DOMAIN PROTEIN family.
  findings:
  - statement: CASPs are plasma-membrane tetraspan proteins that organize a membrane microdomain scaffolding
      Casparian strip lignin deposition in the root endodermis.
- id: file:POPTR/CASP1/CASP1-goa.tsv
  title: QuickGO GOA annotations for CASP1
  findings:
  - statement: GOA contains a single plasma membrane annotation for CASP1.
core_functions:
- description: Plasma membrane scaffold protein that establishes and demarcates the Casparian strip membrane
    domain to direct localized cell wall (lignin) deposition in the root endodermis.
  supported_by:
  - reference_id: file:POPTR/CASP1/CASP1-uniprot.txt
    supporting_text: Required for establishment of the Casparian strip membrane domain (CSD) and the
      subsequent formation of Casparian strips
  locations:
  - id: GO:0005886
    label: plasma membrane
proposed_new_terms: []
suggested_questions:
- question: Is PtCASP1 expressed specifically in the root endodermis and does it localize to a belt-shaped
    Casparian strip domain in Populus as it does in Arabidopsis?
- question: Which lignin-polymerizing enzymes (peroxidases, NADPH oxidases) are recruited to the CASP1
    microdomain in poplar?
suggested_experiments:
- description: Express a fluorescently tagged PtCASP1 in poplar roots and image its subcellular distribution
    relative to lignin deposition to confirm Casparian strip domain localization.
  experiment_type: fluorescence localization
- description: 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.
  experiment_type: targeted functional assay