Cf-4 (O50025, Solanum habrochaites) — curation notes

Identity

• O50025 (TrEMBL, 806 aa) = EMBL CAA05268.1, the Cf-4 (Hcr9-4D) gene from Lycopersicon hirsutum (= S. habrochaites), cloned by Thomas et al. 1997. Signal peptide 1-21, LRR ectodomain, TM 752-776, short cytoplasmic tail, no kinase domain (UniProt features).
• Cf-4 has 25 LRRs vs 27 in Cf-9; >91% identity PMID:9437864
• Cf-4 locus carries five Hcr9 paralogues; Hcr9-4D = Cf-4 (Avr4), Hcr9-4E recognizes Avr4E PMID:15469522
• Cf-4 from L. hirsutum; Cf-4/Cf-9 at the same locus PMID:15166169
• Hcr9-Avr4s conserved across wild tomatoes PMID:16167771

Function

• Specificity determinants in N-terminal domains and LRRs 11-12 PMID:11226184.
• Constitutive complex with SOBIR1; SOBIR1 needed for Cf-4 HR/immunity and Cf-4 stability PMID:23716655
• Avr4 induces BAK1/SERK3 recruitment and endocytosis of Cf-4; Cf-4 at the plasma membrane PMID:26765243
• Direct Cf-4–Avr4 binding not established (deep research: "does not establish a purified-protein binding constant or a resolved direct Cf-4–Avr4 structure"). AVR4 chitin binding belongs to the effector, not Cf-4 (see FULFL/AVR4 review).

Curation decisions

• GO:0038187 pattern recognition receptor activity (EXP, PMID:23716655): definition requires combining with a conserved PAMP. Avr4 is a race-specific effector and direct binding is unproven -> MODIFY to GO:0140376 innate immune receptor activity (already on Cf-4 by EXP; same choice as the CF-9 review).
• GO:0140376 rows: ACCEPT. The PMID:15469522 abstract is about Hcr9-4E/Avr4E, not Cf-4 (Hcr9-4D); full text not cached. Curator (PHI-base) probably used Cf-4 controls; per project rules not removed. Raised as a suggested question.
• GO:0002768 (EXP): ACCEPT (Cf-4 is the receptor initiating the SOBIR1/BAK1 signalling). Consistent with CF-9 NEW row.
• defense response to fungus (ARBA IEA): ACCEPT, consistent with CF-9.
• plasma membrane (IEA): ACCEPT, supported by Postma 2016.
• No NEW rows: all core aspects already present.