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

157 Reversing photoperiodic response by clock mutations in Arabidopsis
Tsuyoshi Mizoguchi 1 , Sumire Fujiwara 1 , Atsushi Oda 1 , Kanae Niinuma 1 , Takeomi Tajima 1 , Riichiro Yoshida 1 , Hiroshi
Kamada 1 , George Coupland 2
1
University of Tsukuba, Japan, 2 Max-Planck Institute for Plant Breeding, Germany
Fluctuations in the length of the day affect developmental processes and behaviors of many organisms. This
phenomenon is called photoperiodism and allows detection of seasonal changes and anticipation of environmental
conditions. In Arabidopsis, LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED 1
(CCA1) each encode a myb protein essential for clock function and play important roles in photoperiodic flowering by
controlling rhythmic expressions of GIGANTEA (GI), CONSTANS (CO) and FLOWERING LOCUS T (FT). Here we
demonstrate a reversal of day-length response by lhy cca1 and propose novel roles of the oscillator components LHY and
CCA1 in clock-dependent and -independent processes in Arabidopsis. We have identified short vegetative phase (svp)
and early flowering 3 (elf3) as suppressor mutations of the late flowering phenotype of the lhy cca1 in continuous light
condition. Functional interaction among LHY, CCA1, SVP and ELF3 will be discussed in more detail.
Mizoguchi et al. Developmental Cell 2002
Mizoguchi et al. Plant Cell 2005
Fujiwara et al. Plant Biotech. 2005a, 2005b, 2005c
Calvino et al. Plant Biotech. 2005
158 DNA Binding Properties of TCP4, a Protein Involved in Leaf Morphogenesis in Arabidopsis
Pooja Aggarwal, Nirmalya Chatterjee, Utpal Nath
Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560 012, India
The TCP family of DNA-binding transcription factors regulate diverse aspects of plant development including
flower asymmetry, plant architecture and leaf morphogenesis. The molecular function of TCP protein is to suppress cell
proliferation in the axillary meristem at very early stage of organ development. CINCINNATA, a TCP gene in Antirrhinum
majus, controls leaf shape and surface curvature by regulating cell proliferation both spatially and temporally. The
Arabidopsis orthologue of CIN, TCP4, also controls leaf morphogenesis the same way CIN does in Antirrhinum.
It has been hypothesized that CIN controls cell proliferation by regulating transcription of its downstream target
genes. However, little is known about what these targets are, in case of CIN or TCP4. We have used Random Binding Site
Selection (RBBS) assay to determine the consensus-binding site of TCP4/CIN, in order to identify their direct targets. We
show that Both TCP4 & CIN bind to the same consensus site GTGGTCCC. By studying the binding properties of TCP4/
CIN with mutated oligos, we show that the core sequence to which these proteins bind to is TGGNCC. The DNA-binding
domain (TCP domain) of TCP4 is predicted to form a basic helix-loop-helix (bHLH) protein. We also demonstrate that
the binding affinity of TCP4 to its target DNA is comparable to other bHLH proteins. Searching the promoter database of
Arabidopsis with the TCP4 consensus site as target sequence has identified many putative direct targets of TCP4. Some
of the direct targets have been validated in planta and their role in TCP4 function will be discussed.