SLAC1 (At1g12480, UniProt Q9LD83) curation notes
Session 1 (2026-10-19)
No deep-research provider was available in this environment, so these notes are
built from the cached publications (publications/PMID_*.md), the UniProt record
and PubMed/E-utilities look-ups. Full text was available for PMID:18305484,
PMID:19955405, PMID:22730405, PMID:20981093, PMID:35523967, PMID:37963863 and
PMID:30361234; the others are abstract-only.
Identity and family
- SLAC1 = SLOW ANION CHANNEL-ASSOCIATED 1, At1g12480, 556 aa, 10 TM helices with
long cytosolic N-terminal (~189 aa) and C-terminal tails. Pfam PF03595 (SLAC1),
InterPro IPR004695 (SLAC1/Mae1/Ssu1/TehA) and IPR030183 (SLAC/SLAH), PANTHER
PTHR31269:SF11 (from the UniProt record).
- Distant homologue of bacterial TehA and fungal Mae1/Ssu1 transporters
PMID:18305482.
- Arabidopsis family: SLAC1 plus SLAH1-SLAH4; SLAH genes can complement slac1 when
driven in guard cells PMID:18305482.
Expression and localization
- Preferentially expressed in guard cells
PMID:18305484.
- Plasma membrane (GFP fusion, onion epidermis, tobacco protoplasts) PMID:18305484; independently
PMID:18305482 (above). BiFC with OST1 in mesophyll protoplasts gives signal only
at the plasma membrane PMID:19955405.
- The ISM nucleus prediction (AtSubP) has no support; SLAC1 is a polytopic PM protein.
Channel activity
- Loss of SLAC1 abolishes guard-cell S-type anion currents (Ca2+- and ABA-activated)
but not R-type or Ca2+ channel currents PMID:18305484.
- Heterologous expression: silent alone; active with OST1 in Xenopus oocytes;
anion-selective, NO3- > Cl- >> malate, HCO3-, SO4 2-; weakly voltage dependent;
not proton-coupled PMID:19955405.
- Structure: trimer, each protomer a 5-helix pore gated by conserved Phe450
(TehA homologue structure + AtSLAC1 mutagenesis) PMID:20981093;
F450A gives large constitutive currents PMID:20981093.
GOA's IDA rows cite this paper by DOI:10.1038/nature09487 = PMID:20981093.
- Cryo-EM of AtSLAC1 (2022, 2023): homotrimer, each subunit an independent pore;
cytosolic N/C-terminal "plug" holds the closed state; phosphorylation releases it
PMID:35523967
PMID:37963863.
BdSLAC1 structure + AtSLAC1 electrophysiology: 14 phosphosites, ~330-fold
activation PMID:33926963.
Regulation by kinases / phosphatases
Physiology (all upstream of the channel; SLAC1 is the effector)
- slac1: stomata insensitive to CO2, ABA, O3, humidity, light/dark, Ca2+, H2O2, NO
PMID:18305484.
- Anion over-accumulation in guard cells of the mutant PMID:18305482.
- 8-nitro-cGMP closure requires SLAC1 PMID:23396828; systemic light-stress
stomatal closure requires SLAC1 PMID:29463779.
- Negative regulation of stomatal opening: SLAC1 inhibits KAT1 (not KAT2) via
protein interaction PMID:27002025
(single study, abstract only). Laanemets et al. PMID:23766366 describe slac1
stomatal opening defects as compensatory feedback (abstract is a single sentence).
Curation decisions (summary)
- Core MF: GO:0008308 voltage-gated monoatomic anion channel activity (matches
modules/abscisic_acid_signaling.yaml). Parent GO:0008509 rows -> MODIFY.
- Core BP: GO:0090332 stomatal closure; transport: GO:0098656, plus Cl- and NO3-
transmembrane transport as refinements of "inorganic anion transport".
- Core CC: plasma membrane; generic "membrane" -> MODIFY; nucleus (ISM) -> REMOVE.
- Bare protein binding: MODIFY to protein kinase binding (OST1, CPK21, CPK23, SIF2)
or potassium channel inhibitor activity (KAT1, AKT2, per UniProt curated text);
REMOVE for GHR1 (pseudokinase), KAT2 (not inhibited) and KC1.
- "Response to X" phenotypes (ABA, CO2, ozone, humidity, light) kept as non-core.
Possible upstream reports
- GO:0005634 nucleus (ISM, GO_REF:0000122, AtSubP) is a false prediction for a
10-TM plasma-membrane channel.
- GO:0090333 regulation of stomatal closure (IMP, PMID:29463779): SLAC1 executes
closure (the anion efflux step) rather than regulating it; GO:0090332 fits.
2026-10-24: OpenScientist run on KAT1/AKT2 inhibition
Report: SLAC1-hypotheses/slac1-kat1-inhibition/openscientist.md (3 iterations, ~25 min).
Hypothesis: SLAC1 directly inhibits KAT1 and AKT2, but not KAT2, and this has been replicated.
- Verdict from the run: partially supported (weak to moderate), not independently replicated.
The report supports keeping GO:0019870 as a non-core activity with caveats.
- Checked here: the Zhang 2016 oocyte result is verbatim in the cached paper
PMID:27002025. The
Laanemets 2013 abstract confirms that slac1 lowers inward K+ channel activity through
raised cytosolic Ca2+ PMID:23126621.
The report calls this "later work"; it is from 2013, three years before Zhang 2016.
- No action changes. The KAT1 and AKT2 rows stay MODIFY with a caveat. KAT1 moves to
GO:0070320 (inward rectifier potassium channel inhibitor activity), matching CBL10's AKT1
row; AKT2 stays on GO:0019870 because it also has non-rectifying gating modes
(PMID:16316977), as decided in the 2026-10-25 ABA module audit below. The report itself only
went as far as GO:0019870, so the KAT1 refinement is a curator decision. The term was
already absent from core_functions.
2026-10-25 — ABA module member audit
Assessed all 44 annotation decisions and channel-centered core functions. Foundational genetics, plasma-membrane localization, heterologous electrophysiology and structure support SLAC1 as an ABA guard-cell anion effector. This does not make guard-cell output universal across land-plant ABA signaling. Core functions remain anion transport and stomatal closure.
Inspected open PR #5402 before editing secondary potassium-channel inhibition rows. KAT1 refinement to GO:0070320 is independently supported by PMID:27002025 and the QuickGO definition (checked 2026-10-25). AKT2 retains broader GO:0019870: primary PMID:16316977 establishes inward-rectifying and nonrectifying gating modes, and available SLAC1 evidence does not resolve which mode was inhibited. This is an intentional evidence-based difference from PR #5402's uniform inward-rectifier replacement. Neither activity is added to core_functions.
PMID:23126621 full text shows that "reducing Ca(2+) to < 10 nM rapidly restored the activity of K(+)(in) channels in slac1 closer to wild-type levels." Loss-of-function physiology involves calcium-dependent compensatory feedback and cannot be treated as a simple direct-inhibition phenotype. Existing heterologous/overexpression inhibitory activity is retained with this limitation; no exhaustive claim about absence of replication is made. PMID:31896774 additionally establishes RAF-SnRK2 input needed for SLAC1 activation after PP2C inactivation.
Research used existing provider reports/manual notes and cached primary literature. All rows retain explicit decisions; unresolved findings are UNDECIDED rather than inferred from missing text. Record-section backfill and targeted validation were run for this session.