The SUMO E3 ligase, AtSIZ1, regulates flowering by controlling a salicylic acid-mediated floral promotion pathway and through affects on FLC chromatin structure.
Loss-of-function siz1 mutations caused early flowering under short days. siz1 plants have elevated salicylic acid (SA) levels, which are restored to wild-type levels by expressing nahG, bacterial salicylate hydroxylase. The early flowering of siz1 was suppressed by expressing nahG, indicating that SIZ1 represses the transition to flowering mainly through suppressing SA-dependent floral promotion signaling under short days. Previous results have shown that exogenous SA treatment does not suppress late flowering of autonomous pathway mutants. However, the siz1 mutation accelerated flowering time of an autonomous pathway mutant, luminidependens, by reducing the expression of FLOWERING LOCUS C (FLC), a floral repressor. This result suggests that SIZ1 promotes FLC expression, possibly through an SA-independent pathway. Evidence indicates that SIZ1 is required for the full activation of FLC expression in the late-flowering FRIGIDA background. Interestingly, increased FLC expression and late flowering of an autonomous pathway mutant, flowering locus d (fld), was not suppressed by siz1, suggesting that SIZ1 promotes FLC expression by repressing FLD. Consistent with this, SIZ1 facilitates sumoylation of FLD that can be suppressed by mutations in three predicted sumoylation motifs in FLD (i.e. FLDK3R). Furthermore, expression of FLDK3R in fld protoplasts strongly reduced FLC transcription compared with expression of FLD, and this affect was linked to reduced acetylation of histone 4 in FLC chromatin. Taken together, the results suggest that SIZ1 is a floral repressor that not only represses the SA-dependent pathway, but also promotes FLC expression by repressing FLD activity through sumoylation, which is required for full FLC expression in a FRIGIDA background.
Jin
Jing Bo
JB
Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907 2010, USA.
Jin
Yin Hua
YH
Lee
Jiyoung
J
Miura
Kenji
K
Yoo
Chan Yul
CY
Kim
Woe-Yeon
WY
Van Oosten
Michael
M
Hyun
Youbong
Y
Somers
David E
DE
Lee
Ilha
I
Yun
Dae-Jin
DJ
Bressan
Ray A
RA
Hasegawa
Paul M
PM
D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D035264:Flowers / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D008025:Ligases / Q000235:genetics / Q000378:metabolism*; D026161:MADS Domain Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020156:Salicylic Acid / Q000378:metabolism*
D029681:Arabidopsis Proteins; C418902:At5g10140 protein, Arabidopsis; D026161:MADS Domain Proteins; C479923:flowering locus D protein, Arabidopsis; D006655:Histone Deacetylases; D008025:Ligases; C502552:SIZ1 protein, Arabidopsis; D020156:Salicylic Acid