75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

151 Dissection of Flowering Pathways Using a GL2-class HD-ZIP Protein FWA
Yoko Ikeda, Ayako Yamaguchi, Mitsutomo Abe, Takashi Araki
Department of Botany, Graduate School of Science, Kyoto University
Late-flowering mutant fwa is a dominant epigenetic mutant that ectopically expresses a GL2-type HD-ZIP gene due
to promoter hypomethylation. Previous genetic analysis suggests that FWA blocks the flowering pathway at FT and/or
downstream of FT. We envisage that FWA may provide a unique tool to dissect pathway from FT to flowering. Therefore,
we investigated the mechanism by which ectopic FWA causes late flowering phenotype. First, we tested the possibility
that FWA inhibits flowering through the transcriptional mis-regulation of target genes. We performed microarray analysis
using two independent fwa epialleles and a 35S::FWA line. The transcriptional profiles of these plants suggest that
late-flowering phenotype of fwa is unlikely due to the mis-regulation of transcription. Next, we examined interaction
of FWA protein with known flowering regulators such as FT, TSF, TFL1 and FD. FWA protein strongly interacted with
FT protein through its C-terminal region and ZIP domain in yeast cells. No interaction was observed between FWA and
TSF, FWA and TFL1, and FWA and FD. Interaction between FWA and FT was confirmed by in-vitro pull down assay.
C-terminal truncation of FWA abolished interaction with FT. Overexpression of FWA with truncated C-terminus did not
cause late-flowering phenotype. These suggest that ectopically-expressed FWA inhibits floral transition by interfering
with the FT function through protein-protein interaction. Based on this, we investigated the site of action of FT protein
using FWA protein as a specific inhibitor of the FT protein function. We examined the tissue where FWA can exert its
negative effect on flowering. FWA expressed in the shoot apex by FD promoter delayed flowering, while FWA expressed
in the vascular tissues (including the phloem cells which express FT) did not. These results strongly suggest that FT
protein acts in the shoot apex.
152 Arabidopsis SUMO-E3 ligase, AtSIZ1 Negatively Regulates Flowering Time Dependent of
Autonomous and SA pathway
Jing Bo Jin 1 , Yin Hua Jin 1 , Ji Young Lee 2 , Kenji Miura 1 , Chan Yul Yoo 1 , Dae-Jin Yun 2 , Ilha Lee 3 , Ray Bressan 1 , Paul
Hasegawa 1
1
Purdue.University, 2 Gyeongsang National University, 3 Seoul National University
Small ubiquitin-like modifier (SUMO) conjugation plays critical roles in many cellular processes. We have determined
that AtSIZ1 is a negative regulator of flowering time through a salicylic acid (SA)-dependent and the autonomous pathways.
siz1-2 and siz1-3 plants exhibit early flowering under short days , but only a modicum of earliness under long days.siz1
does not alter circadian rhythm-dependent and CO or GI expression patterns relative to wild type and flowering of siz1
plants is accelerated to a similar extent as wild type in response to vernalization and GA treatments. Quantitative (q) PCR
determination of transcript abundance and genetic analysis of double mutants (siz1-2 ft-1 and siz1-2 soc1-2) indicate
that early flowering is attributable to FT and SOC1. siz1 plants have constitutively elevated SA levels and NahG reduces
SA levels and partially suppresses early flowering of siz1-2 (i.e., siz1-2 NahG) plants. Early flowering of siz1 plants is
linked to reduced FLC transcript abundance but FLM and MAF2 mRNA levels are similar to wild type. Flowering time
evaluation of siz1-2, flc-3 and siz1-2 flc-3 plants flower earlier than single parental plant, indicates that early flowering
phenotype of siz1 is partially FLC-dependent and SA might be the second factor. Analysis of genetic interaction between
several autonomous pathway genes (such as LD, FCA and FVE) and SIZ1, have shown that early flowering phenotype
of siz1 is suppressed by mutation in autonomous pathway genes (ld-1, fca-9 and fve-3). These results indicate that downregulation
of FLC mRNA abundance in siz1 is autonomous pathway dependent.