LYM2 (At2g17120, UniProt O23006) curation notes

Identity

• LysM domain-containing GPI-anchored protein 2; also called AtCEBiP / CEBiP-like1. Closest
  Arabidopsis homologue of rice OsCEBiP. UniProt: signal peptide 1-23, two annotated LysM
  domains (108-155, 172-216), GPI-anchor at D318, C-terminal propeptide removed; no
  transmembrane or intracellular domain.
• Deep research (falcon) available: LYM2-deep-research-falcon.md; consistent with primary papers.
• Note that "CEBiP-like1" in Petutschnig 2010 / Wan 2012 is LYM2: PMID:20610395.

Molecular function: chitin binding

• PMID:22891159 (abstract only in cache)
• PMID:22891159
• Chitin bead pulldowns: PMID:22744984 — basis for the TAIR IDA.
• LYM1/LYM3 do not bind chitin (they act in peptidoglycan perception with CERK1).

Not required for canonical CERK1 chitin signalling

• PMID:22891159
• PMID:22744984
• PMID:23674687
• So the rice OsCEBiP-OsCERK1 model does not transfer to Arabidopsis; in Arabidopsis LYK5 is the high-affinity chitin receptor that recruits CERK1 (see genes/ARATH/LYK5).

Chitin-triggered plasmodesmal closure

• PMID:23674687
• CERK1 not required: PMID:23674687
• Localization: PMID:23674687
• Mechanism (Cheval 2020): requires LYK4, LYK5, RBOHD (Ser133), CPK6, CPK11; callose deposition. PMID:32284410
• PMID:32284410
• PMID:32284410
• LYM2 lacks intracellular domains: PMID:32284410
• Poplar orthologues do the same (PMID:42516602), suggesting conservation in dicots.

Defense against fungi

• Botrytis: PMID:23674687
• Alternaria brassicicola: PMID:23803749
• Not required against Pto DC3000: PMID:23674687

GOA observations

• GOA has NO biological process annotation for LYM2 at all (and OsCEBiP also has none),
  despite clear mutant data from Faulkner 2013 and Cheval 2020. LYK5 carries
  cellular response to chitin (IBA, IEP) and innate immune response (IMP).
• Mitochondrion HDA (PMID:28887381) is a co-fractionation profiling call; contradicted by
  the signal peptide/GPI anchor and imaging. Removed.
• Plasma membrane / plasmodesma rows all consistent with imaging (PMID:23674687).
• GO lacks a term for regulation of plasmodesmata-mediated intercellular transport; proposed.

Decisions

• NEW: GO:0071323 cellular response to chitin (IMP, PMID:23674687). Participation test: LYM2
  is the chitin-binding receptor component for this response (it performs ligand perception),
  not merely a required downstream component. Comparator: LYK5 and CERK1 (chitin-binding LysM
  receptors) carry chitin-response terms.
• NEW: GO:0050832 defense response to fungus not added — evidence is infection phenotype
  (necessity); recorded as non-asserted context and in questions.