Plant Physiology Preview
Published on March 23, 2007; 10.1104/pp.107.097048
OPEN ACCESS ARTICLE
Received February 1, 2007
Accepted March 15, 2007
GIGANTEA Regulates Phytochrome A-mediated Photomorphogenesis Independently of its Role in the Circadian Clock
Karina Andrea Oliverio , María Crepy , Ellen L. Martin-Tryon , Raechel Milich , Stacey L. Harmer , Jo Putterill , Marcelo J. Yanovsky , and Jorge J. Casal *
IFEVA, Facultad de Agronomía, Universidad de Buenos Aires and Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Section of Plant Biology, College of Biological Sciences, University of California, Davis, California; School of Biological Sciences, University of Auckland, Auckland, New Zealand
* Corresponding author; email: casal{at}ifeva.edu.ar.
GIGANTEA (GI) is a nuclear protein involved in the promotion of flowering by long days, in light input to the circadian clock and in seedling photomorphogenesis under continuous red but not far-red light. Here we report that in Arabidopsis thaliana different alleles of gi have defects in the hypocotyl-growth and cotyledon-unfolding responses to hourly pulses of far-red light, a treatment perceived by phytochrome A (phyA). This phenotype is rescued by overexpression of GI. The very-low-fluence response of seed germination was also reduced in gi. Since the circadian clock modulates many light responses, we investigated whether these gi phenotypes were due to alterations in the circadian system or light signalling per se. In experiments where far-red light pulses were given to dark-incubated seeds or seedlings at different times of the day, gi showed reduced seed germination, cotyledon unfolding and activity of a luciferase reporter fused to the promoter of a chlorophyll a/b binding protein gene; however, rhythmic sensitivity was normal in these plants. We conclude that while GI does not affect the high-irradiance responses of phyA, it does affect phyA-mediated very-low-fluence responses via mechanisms that do not obviously involve its circadian functions.
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