SIZ1 (Arabidopsis thaliana, Q680Q4, At5g60410) - curation notes

Identity and family

Sole Arabidopsis Siz/PIAS (SP-RING) SUMO E3; PANTHER PTHR10782:SF102 (E3 SUMO-PROTEIN LIGASE SIZ1).
PMID:19837819
Domains: SAP (11-45), PHD-type zinc finger (112-168, plant-specific), PINIT, SP-RING (346-429, Zn ligands C379/H381/C402/C405), SXS. (UniProt features; PMID:19837819)
PHD finger binds SCE1 (E2) and is needed for GTE3 sumoylation PMID:18502747.

Biochemistry

In vitro E3 activity; global sumoylation impaired in siz1 PMID:15894620
Heat-induced SUMO1/2 conjugation largely SIZ1-dependent and nuclear PMID:17644626
SUMO1/SUMO2 preference; splice variant SSV2 is plasma-membrane localized and sumoylates CNGC6 PMID:38497423
SP-RING needed for activity and nuclear localization PMID:19837819

Localization

Nuclear foci / speckles PMID:15894620; PMID:15894620.

Substrates with mapped mechanism (basis for "does the work" judgements)

Substrate	Process	Evidence
PHR1 (K261/K372)	Pi starvation	PMID:15894620
ICE1 K393	cold/freezing	PMID:17416732
ABI5 K391	ABA (negative)	PMID:19276109
MYB30 K283	ABA	PMID:22814374
FLD	flowering (FLC)	PMID:18069938
NIA1/NIA2	nitrate assimilation	PMID:21772271
GTE3, SCE1, self	-	PMID:18502747
NF-YC10	heat	PMID:36282496
MAC components	immunity (positive, when overaccumulated)	PMID:41986387

Phenotype-only / indirect roles

SA hyperaccumulation, constitutive SAR, PAD4-dependent; JA arm unaffected PMID:17163880
Dwarfism, cell size/number reduction is SA-dependent PMID:20007967 -> cell division and unidimensional cell growth marked over-annotated.
Basal NOT acquired thermotolerance PMID:17041025 -> heat acclimation MODIFY to response to heat.
Drought PMID:17905899
Female gametophyte degeneration after FG7; pollen tube guidance defect is secondary; SIZ1 not expressed in pollen PMID:22253727
Shoot regeneration repressed PMID:32611787.
Pi: wild-type internal Pi in siz1 PMID:15894620 -> "detection of phosphate ion" is a sensor claim not supported; MODIFY to regulation of cellular response to phosphate starvation.

Decisions summary

protein binding: SCE1 row MODIFY -> GO:0044390 ubiquitin-like protein conjugating enzyme binding; GTE3/GTE5 rows REMOVE (substrate interactions; covered by SUMO transferase/sumoylation).
innate immune response-activating signaling pathway -> MODIFY to GO:2000031 regulation of SA mediated signaling pathway (no negative-regulation term exists in GO; SIZ1 also has a positive context-dependent role per PMID:41986387).
regulation of ABA signaling -> MODIFY to GO:0009788 negative regulation.
No NEW annotations proposed: candidate processes (heat response via NF-YC10, immune condensates) are either covered by MODIFY replacements or rest on single recent studies.

Deep research verification

OpenScientist report claims checked against cached primary papers listed above. Not verified (no cached text): HAT1 (PMID:42260756), AL6 (PMID:39562527), HLS1 (PMID:36890719), FLC stabilization (PMID:24218331), COP1/VPS29 regulation of SIZ1 (PMID:28979848, PMID:40286281), cadmium (PMID:35718335); these were not used for annotation decisions.