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

395 Functional analysis of phosphatidic acid during germination
Takeshi Katagiri, Kazuo Shinozaki
Plant Molecular Biology Laboratory, RIKEN Tsukuba Institute
Phosphatidic acid (PA) has been proposed to function as a lipid signaling molecule in plants. Physiological analysis
showed that PA triggers early signal transduction events that lead to responses to abscisic acid ( ABA ) during seed
germination. In a previous study, using PA-catabolic enzyme lipid phosphate phosphatase (LPP) knockout mutant, we
measured PA production during seed germination and found increased PA levels during early germination (1). In this
study, we focused on the PA-synthetic enzyme phospholipase D (PLD) and showed which PLD functions specifically on
this process with each PLD T-DNA insertional mutant. The PLD knockout mutant showed ABA insensitive germination.
This result confirmed that PA is involved in ABA signaling. Moreover, to determine several target genes downstream of
PA, we performed microarray analysis on the PLD mutant during germination. We discuss about PA signaling pathway
that involved in ABA signaling during germination.
(1) Katagiri et al., Plant J 43, 107-117, 2005
396 COG1, cogwheel in light signaling represses photoperiodic flowering time in Arabidopsis
by an antagonistic interaction with GIGANTEA
Jeongsik Kim 1 , Yumi Kim 1 , Donha Park 2 , Pyung Ok Lim 3 , Miji Yeom 1 , Hong Gil Nam 1
1
Division of Molecular and Life Sciences, Pohang University of Science and Technology, Pohang, Kyungbuk,
790-784, Republic of Korea, 2 Department of Plant Biology/Plant Biotechnology Center, Ohio State University,
Columbus, OH 43210, USA, 3 Faculty of Science Education, Cheju National University, 66 Jejudaehakno, Jejusi,
Jeju-do, 690-756, Republic of Korea.
Higher plants use day-length or photoperiod as an environmental cue to regulate many aspects of development
including the transition from vegetative to reproductive stage. The control of flowering by day length is achieved by
fine molecular regulations of CONSTANS (CO), a key molecule in control of photoperiodic flowering. GIGANTEA
(GI) is largely believed to a major factor regulating CO transcripts in long days under circadian clock control, but
understandings of its molecular mechanisms are largely unknown. COG1, cogwheel1 in light signaling, was reported
to be a phytochrome-signaling component that acts as a light repressor of photomorphogensis in Arabidopsis. cog1-1D
and cog1-2D also exhibited an extremely late flowering phenotype in long day condition, not in short day condition. In
agreement with flowering phenotypes, the rhythmic expression of CO and FT in long-day condition was decreased. Based
on genetic and molecular approaches, inhibition of flowering time by COG1 in long days is not due to the aberrant clock
function, but due to the direct repression of CO promoter activity. Taken together, COG1 directly interacted with GI in
yeast and in mesophyll protoplast, supporting that COG1 controls photoperiodic flowering time by direct repression of
CO transcripts through inhibitory interaction with GI directly.