AS1 (ASYMMETRIC LEAVES1, MYB91, At2g37630; UniProt O80931) - manual literature synthesis

No deep-research API was available for this review; this synthesis was written by the
reviewer from the cached publications in publications/ and the UniProt record
(AS1-uniprot.txt). Every claim carries its provenance.

Identity and domain architecture

• AS1 is a 367-aa R2R3-type MYB-domain protein, the Arabidopsis ortholog of Antirrhinum
  PHANTASTICA and maize ROUGH SHEATH2 PMID:11882937. UniProt annotates two HTH myb-type domains (residues 1-53 and 54-108;
  PROSITE PS51294, Pfam PF13921) and places AS1 in PANTHER PTHR47214 (PROTEIN ROUGH SHEATH 2
  HOMOLOG), subfamily SF3 (TRANSCRIPTION FACTOR AS1).
• The MYB domain is diverged: "several of the amino acids in the third helix of the R3 MYB
  motif that are critical for MYB-DNA interaction are not conserved in AS1, and attempts to
  demonstrate binding of this protein to DNA in vitro have thus far been unsuccessful"
  PMID:18203921.
• A conserved C-terminal domain mediates homodimerization PMID:12750468.

Molecular function: DNA-binding repressor acting with AS2

• AS1 and the LOB-domain protein AS2 (LBD6) form a repressor complex that binds two sites
  (motifs CWGTTD and KMKTTGAHW) in the BP/KNAT1 and KNAT2 promoters; ChIP shows in vivo
  occupancy PMID:18203921.
• AS1 alone and AS2 alone do not bind in EMSA; only co-translated AS1+AS2 bind
  [PMID:18203921 "When translated separately, neither AS1 nor AS2 was able to bind fragment X
  in vitro"; "when AS1 and AS2 were cotranslated, these proteins were able to bind as a
  complex to site X of the BP promoter"]. DNA binding is therefore a property of the
  heterodimer, to which AS1 contributes.
• AS1 interacts with HDA6 and with HIRA; HDA6 and AS1 both occupy KNAT1, KNAT2 and KNATM
  chromatin, and KNOX loci are hyperacetylated in hda6 [PMID:23271976 "Chromatin
  immunoprecipitation assays revealed that HDA6 and AS1 bound directly to KNAT1, KNAT2, and
  KNATM chromatin"; PMID:16243907 "RS2/AS1 can form conserved protein complexes through
  interaction with the DNA binding factor ASYMMETRIC LEAVES2, a predicted RNA binding protein
  (RIK, for RS2-Interacting KH protein), and a homologue of the chromatin-remodeling protein
  HIRA"].
• AS1 also acts as an activator in at least one context: it complexes with CONSTANS and binds
  the FT promoter in vivo; as1 mutants have reduced FT and delayed flowering
  PMID:21950734.
• AS1 binds promoters of jasmonate-responsive genes and dampens necrotroph defense
  PMID:18003921.
• High-throughput yeast one-hybrid screens recorded AS1 binding to promoters of
  glucosinolate, secondary-cell-wall, nitrogen-metabolism and vascular genes
  (PMID:25352272, PMID:25533953, PMID:30356219, PMID:31806676); these are unvalidated for AS1.

Localization

• Nuclear [PMID:23271976, BiFC "HDA6 interacted with AS1 in the nucleus of as2-1 mutants"].
• YFP-AS1 alone is predominantly nucleolar; with AS2 the two co-localize in nucleolus and
  nucleoplasm; AS1 associates with condensed metaphase chromosomes [PMID:18713400 "AS1 and AS2
  alone were predominantly localized in the nucleolus and the nucleoplasm, respectively";
  "AS1 alone was able to associate with the condensed chromosome in the metaphase cell"].
  AS1/AS2 co-localize in subnuclear bodies adjacent to the nucleolus PMID:17293570.

Biological roles

• Represses class I KNOX genes (BP/KNAT1, KNAT2, KNAT6, KNATM) in leaf primordia, separating
  organ founder cells from stem cells [PMID:11140682 "AS1 negatively regulates the homeobox
  genes KNAT1 and KNAT2"; PMID:11076771 "AS1 and AS2 promote leaf differentiation through
  repression of knox expression in leaves"].
• Leaf adaxial-abaxial polarity, with AS2, ERECTA, HDACs and the nucleolar RH10 helicase,
  through repression of abaxial genes ETT/ARF3 and ARF4 [PMID:12874130; PMID:17293570;
  PMID:27334696 "the epigenetic repressor complex of ASYMMETRIC-LEAVES1 (AS1) and AS2 (AS1-AS2)
  is critical to repress abaxial (ventral) genes ETT/ARF3 and ARF4"].
• Leaf morphogenesis/proximodistal patterning and leaf initiation in combination with auxin
  [PMID:11882937; PMID:16971475 "auxin and AS1 pathways converge to repress expression of the
  KNOX gene BREVIPEDICELLUS (BP) and thus promote leaf fate"].
• Fruit mediolateral patterning as a lateral factor repressing BP PMID:23133401.
• Pathogen responses independent of AS2: negative regulator of JA-dependent resistance to
  necrotrophic fungi, positive regulator of SA-independent defense to bacteria PMID:18003921.
• Target of the geminivirus betaC1 pathogenicity factor PMID:18794352.