IAMH1 (AT4G37550) curation notes

Identity

• Locus AT4G37550. There are seven unreviewed UniProt entries for this locus (B9DFI3, Q9SZE9, F4JS37, F4JS39,
  A0A178UXH8, A0A1P8B5Z2, A0A1P8B5Z4), corresponding to alternative gene models. I used A0A178UXH8 (456 aa,
  reference proteome UP000006548) because it is the entry that carries TAIR's GO annotations; the other
  entries carry only the InterPro2GO IEA row (QuickGO, 2026-10-21).
• Symbol IAMH1 (INDOLE-3-ACETAMIDE HYDROLASE 1) was assigned by Gao et al. 2020
  PMID:32327358.
• Tandem paralog of IAMH2 (AT4G37560), 90% identical PMID:32327358.
  See genes/ARATH/IAMH2/IAMH2-notes.md for the shared family and domain analysis.

Deep research

Automated deep research (just deep-research-falcon ARATH IAMH1 --fallback perplexity-lite) failed in this
session because no provider API keys were available. The literature was searched manually through PubMed;
PMID:32327358 is the only primary functional paper on IAMH1. PMID:42844995 (2026) is about IAMH2 but
discusses IAMH1 as background.

Function evidence (Gao et al. 2020, PMID:32327358; full text read)

• Isolated from an EMS forward screen for IAM-insensitive mutants that keep normal auxin sensitivity. The
  allele iamh1-1 carries a premature stop codon; a T-DNA allele (iamh1-2) is also IAM-resistant.
• Complementation with the genomic fragment and with IAMH1pro:IAMH1-GFP:
  PMID:32327358
  PMID:32327358
• Expression: PMID:32327358
  At the reproductive stage, GUS was seen in young flowers, gynoecia and inflorescences.
• Localization: PMID:32327358
  The cached text describes the signal only as non-nuclear and does not name another compartment.
• Double mutants iamh1-1 iamh2-2 and iamh1-1 iamh2-3 suppress iaaM-driven auxin overproduction and the
  IAM-induced rise in IAA and IAA conjugates, but have no developmental defect under normal growth conditions.
  Steady-state IAA is similar to wild type.
• I found no in vitro enzyme assay with purified IAMH1.
• Orthologs: PMID:32327358

Additional evidence from X. Gao et al. 2026 (PMID:42844995) and Moya-Cuevas et al. (PMID:41362017)

Added after the automated PR review (2026-10-22).
- IAMH1-specific data in the IAMH2 paper:
PMID:42844995
PMID:42844995
Figure S3A of the same paper shows At4g37550 allelic variation between the Sichuan and Tibet ecotypes.
So IAMH1 and IAMH2 are redundant for exogenous or iaaM-derived IAM, but not for low-light hypocotyl growth.
- Pathway caveat: PMID:42844995,
citing Moya-Cuevas et al. 2026. I resolved that citation through PubMed to PMID:41362017 (New Phytol
249:2452-2466; DOI 10.1111/nph.70819) and read the full text. It never mentions IAMH1 or IAMH2. It
proposes that IAM acts as a signal through ABA:
PMID:41362017
and describes the IAM pathway as contributing to IAA "under specific conditions". This qualifies but
does not refute the IAM-to-IAA role of the IAMHs, so the NEW GO:0009684 annotation is kept with the
caveat recorded in its reason.

GO annotation decisions (summary)

• GO:0016811 (IEA): MODIFY to GO:0043864 indoleacetamide hydrolase activity (a descendant; OLS checked).
• GO:0005829 cytosol (HDA, Aryal et al. 2014): ACCEPT. It fits the non-nuclear GFP signal of a soluble
  enzyme without targeting signals.
• GO:0000325 plant-type vacuole (HDA, Carter et al. 2004 vegetative vacuole proteome) and
  GO:0005886 plasma membrane (HDA, membrane protein-correlation profiling, PMID:28887381): UNDECIDED,
  at the user's request (2026-10-22). These high-throughput detections are not judged in this review
  because the per-protein data were not examined. Context for a later reviewer:
• The vacuole paper itself notes contaminants in the preparation (it excluded 15% of hits as potential
  chloroplast or mitochondrial contaminants).
• The membrane study found many soluble proteins partitioned between cytosolic and membrane-associated pools.
• The cytosol HDA row stays ACCEPT because it agrees with the IAMH1-GFP data and supports the core function.
• GO:0009507 chloroplast (ISM, AtSubP prediction): MARK_AS_OVER_ANNOTATED.
• It is a single sequence-based prediction with no experimental support.
• None of the three proteomic datasets places IAMH1 in plastids.
• Correction (2026-10-22, after PR review): an earlier version argued that the first 80 residues of
  IAMH1 and IAMH2 are "nearly identical". That was wrong. Computed from the two UniProt sequences they
  differ at 21 of 80 positions (73.75% identity), less conserved than the 90% full-length identity, so
  no N-terminal (transit-peptide) argument can be made from IAMH2's lack of a chloroplast annotation.
  The sentence was removed from the review.
• NEW GO:0009684 indoleacetic acid biosynthetic process (IMP, PMID:32327358).
• Participation: IAMH1 is proposed to catalyse IAM to IAA, so it performs a step of the process.
• Evidence: genetic and metabolite data. Comparator AMI1 carries GO:0009684 by IDA (QuickGO, taxon 3702).
• Caveat: the evidence concerns IAM supplied exogenously or produced from the iaaM transgene. Endogenous
  IAA is unchanged in the double mutant.