CAT2 (At4g35090; UniProt P25819) - curation notes

Deep research could not be run for this gene (no deep-research provider API keys in this
environment). These notes were built only from cached publications (publications/PMID_*.md),
the UniProt record (CAT2-uniprot.txt) and papers cached with ai-gene-review fetch-pmid.
No -deep-research-*.md file exists for this gene.

Identity

• CATALASE2, At4g35090, 492 aa, monofunctional heme catalase (catalase family; PANTHER
  PTHR11465:SF23; Pfam PF00199 and PF06628). One of three Arabidopsis catalases (CAT1
  At1g20630, CAT2 At4g35090, CAT3 At1g20620).

Molecular function

• Catalase (EC 1.11.1.6), 2 H2O2 = O2 + 2 H2O; UniProt function statement is by similarity to
  human catalase P04040 [file:ARATH/CAT2/CAT2-uniprot.txt "Catalyzes the degradation of
  hydrogen peroxide (H(2)O(2)) generated by peroxisomal oxidases to water and oxygen, thereby
  protecting cells from the toxic effects of hydrogen peroxide."]. Heme cofactor (by similarity).
• CAT2 provides most leaf catalase activity: PMID:25700484 and PMID:25700484.
• Recombinant CAT2 is active, mainly as a tetramer PMID:25700484.
• Forward genetics: hydroxyurea-resistant EMS mutants are CAT2 alleles with reduced catalase
  activity PMID:20452979,
  PMID:20452979. HU inhibits catalase PMID:20452979.
• Catalase-deficient (CAT2-deficient) transgenic lines: PMID:15200641
  (abstract only; the abstract does not itself name CAT2).

Assembly, chaperone and partners

• NO CATALASE ACTIVITY1 (NCA1) is a chaperone required for catalase activity; it binds CAT2 1:1
  in the cytosol and increases its activity PMID:25700484, PMID:25700484.
• Other reported partners (not adjudicated as specific MFs): NDK1 (yeast two-hybrid,
  PMID:14581623), 14-3-3 omega TAP-MS (PMID:19452453), LSD1, which interacts with all three catalases
  PMID:23958864.

Localization

• Peroxisome (matrix): PMID:25700484; CAT2 detected in leaf peroxisomes (PMID:17951448).
  UniProt: cytosol and peroxisome matrix, both from PMID:25700484.
• A cytosolic pool exists before/while being folded by NCA1 (BiFC in cytosol, PMID:25700484). This
  contradicts the GOA NOT cytosol (RCA, PMID:21166475) row.
• Mitochondrion, plasma membrane, stromule, cytosolic ribosome detections come from bulk
  proteomics and are most likely carry-over of this abundant peroxisomal protein.

Biological process

• Photorespiration: PMID:22303256 and PMID:22303256.
• cat2 knockout is a conditional photorespiratory mutant PMID:17877712. Day length controls lesion formation in cat2 (photoperiod-dependent cell
  death), which is a conditional phenotype of the mutant rather than a role of CAT2 in
  photoperiodism.
• cat2 is a widely used model of intracellular H2O2 stress (review PMID:20876333, abstract only).
• Second-site gox1 mutation attenuates the cat2 phenotype PMID:27225899, placing CAT2 downstream of GOX1 H2O2
  production.
• Expression: light-stimulated and clock regulated (PMID:22303256 citing Zhong et al. 1997);
  cat2 mRNA increased under sulfur depletion (PMID:15032878); CAT2 transcripts up after cold
  and dark treatments (PMID:18230142: "clearly up regulated after all three treatments i.e.
  under the Cold/Light, Cold/Dark and Dark conditions"). These are expression responses, not
  evidence of participation.

GO term checks (OLS4)

• GO:0004096 catalase activity; GO:0042744 hydrogen peroxide catabolic process; GO:0098869
  cellular oxidant detoxification; GO:0005782 peroxisomal matrix; GO:0009853 photorespiration
  (parent of GO:0009854 oxidative photosynthetic carbon pathway). All current.
• QuickGO (2026-10-20): no catalase of any species carries GO:0009853 or descendants; the only
  experimental photorespiration annotations outside Arabidopsis are rice GLO1. In Arabidopsis,
  photorespiration is carried by GLU1, GLYK, HPR, SHM1, PLGG1, PEX10, PUMP1 and others (IMP/TAS).
  The absence for CAT2 is therefore not a systematic cross-species convention with a body of
  experimental catalase annotations behind it. A NEW photorespiration row was first proposed
  on that basis, then withdrawn on curator review (2026-10-22, PR #5254): H2O2 removal is
  ancillary to the carbon chemistry of the cycle, and the systematic absence of the term from
  catalases is treated as a convention. CAT2 is linked to the pathway through GO:0042744
  hydrogen peroxide catabolic process, and the question is kept in suggested_questions.

Module comparison (modules/photorespiration_c2_cycle.yaml)

• Module: GO:0004096 catalase activity, GO:0009853 photorespiration, GO:0005777 peroxisome.
  Review agrees on MF and process; for location the more specific GO:0005782 peroxisomal matrix
  is supported (EXP) and used in core_functions.