75 Integrating Membrane Transport with Male Gametophyte ... - TAIR
75 Integrating Membrane Transport with Male Gametophyte ... - TAIR
75 Integrating Membrane Transport with Male Gametophyte ... - TAIR
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145 Cryptochrome 2 (cry2) in Vascular Bundles Regulates Flowering in Arabidopsis<br />
Motomu Endo, Nobuyoshi Mochizuki, Tomomi Suzuki, Akira Nagatani<br />
Laboratory of Plant Physiology, Graduate School of Science, Kyoto University, Kyoto, Japan<br />
Light is one of the most important stimuli to trigger the transition from vegetative phase to reproductive phase,<br />
namely flowering. In Arabidopsis, phytochrome B (phyB) and cryptochrome 2 (cry2) are major photoreceptors to regulate<br />
flowering time. Both are known to be expressed in almost all organs/tissues. It has been well-known since 1937 that<br />
plants perceive the light stimuli only in leaves to regulate flowering. Hence, photoreceptors in restricted parts can regulate<br />
flowering. We have investigated this issue and demonstrated that phyB regulates flowering time only in mesophyll cells<br />
(Endo et al., 2005). However it had remained unclear where cry2 regulates flowering.<br />
Here, we expressed a cry2-GFP fusion protein in the cry2 mutant background in organ/tissue specific manners by using<br />
specific promoters. We confirmed that cry2-GFP was expressed in expected places for all the promoters. Immunoblot,<br />
GFP fluorescence and real time PCR analyses demonstrated that the expression levels in respective organs/tissues in<br />
these lines were comparable to those of the authentic cry2. Transgenic lines expressing cry2-GFP in vascular bundles<br />
exhibited full complementation of the late flowering phenotype. By contrast, the other lines that expressed cry2-GFP in<br />
mesophyll, epidermis, SAM or root flowered late. FT is a key positive regulator of flowering. It is expressed in vascular<br />
bundles. We examined FT regulation by cry2 at the tissue level. In the lines expressing cry2-GFP in vascular bundles, FT<br />
mRNA was increased in vascular bundles. As expected, no induction of the FT expression was observed in other lines.<br />
Hence, only cry2 in vascular bundle regulates FT expression, which takes place in vascular bundles.<br />
146 Analysis ff Natural Genetic Variation in Photoperiodic Regulation of Flowering Time in<br />
Arabidopsis Thaliana<br />
Antonis Giakountis, Frederic Cremer, George Coupland<br />
Max Planck Institute For Plant Breeding Research, Carl-von-Linne weg 10, D-50829 Cologne, Germany<br />
Plants utilize a variety of endogenous signals and external stimuli to regulate the transition from vegetative growth<br />
to flowering. In Arabidopsis, GIGANTEA (GI) a clock output gene expressed in the evening, is considered to mediate<br />
between the circadian clock and transcription of CONSTANS (CO), another major gene of the photoperiod pathway.<br />
Upon exposure to inductive long-day conditions CO expression is up-regulated and in the presence of blue and far-red<br />
light, the stabilized CO protein activates the expression of the downstream floral integrator FT.<br />
The effect of photoperiod on flowering-time control of Arabidopsis has been studied by analyzing flowering under<br />
extreme photoperiods of 8-10 h and 16 h, however under natural conditions photoperiod varies continuously <strong>with</strong> the<br />
changing seasons. We have described the flowering-time behaviour of model accessions such as Columbia and Ler at 6<br />
different daylengths. Natural variation between accessions has been widely used as a tool for functional genetics, allowing<br />
the identification of genetic and/or allelic variation for a trait of interest. We have used two collections of Arabidopsis<br />
accessions in order to identify natural variation in their flowering time responses under a wide range of photoperiods. In<br />
addition forty transgenic lines of flowering time genes have been included in the analysis and their photoperiod responses<br />
are compared <strong>with</strong> those of the accessions. In order to evaluate the contribution of the circadian clock in photoperiod<br />
discrimination, the same accessions were transformed <strong>with</strong> a promoter fusion of GI to the firefly luciferase gene.<br />
A two way ANOVA approach revealed the presence of extensive natural variation in the flowering time responses of<br />
accessions under different photoperiods. By performing a real time monitoring of the bioluminescence under the same<br />
range of photoperiods as for flowering time, we were able to identify additional natural variation in the peak time of GI<br />
expression under different daylengths. A selection of interesting accessions was made and expression analysis of several<br />
genes of the photoperiod pathway together <strong>with</strong> QTL mapping are in progress in an attempt to identify the sources of<br />
the observed natural variation at the molecular level.