Chen, Meng , Chory, Joanne .
HEMERA: a novel regulator required for phytochrome nuclear body localization and photomorphogenesis in Arabidopsis.
Phytochromes, the red and far-red photoreceptors, regulate every facet of plant growth and development in response to environmental light cues. One striking effects of light at the cellular level is the rapid and reversible nuclear localization of phytochromes themselves. Within the nucleus, phytochrome B (phyB), the most prominent phytochrome in Arabidopsis, is further compartmentalized to stable discrete subnuclear domains, referred to as phyB nuclear bodies (NBs). Though the formation of phyB NBs is closely correlated to phyB responses, the precise function of phyB NBs is unknown. To isolate extrinsic factors required for phyB NB formation, we initiated a confocal-based genetic screen for phyB:GFP mislocalization mutants. Hemera-1 (hmr-1), one mutant identified from the screen, does not form or only forms small phyB:GFP NBs in growing epidermal cells of the hypocotyl. We cloned HMR by a map-based cloning method. HMR encodes a novel protein that is conserved across land plants. In addition to subcellular phenotypes in phyB NBs, hmr mutants show dramatic hyposensitivity specifically to red and far-red light. Physiological characterization of hmr mutants demonstrated that HMR is required for all of phyB and phyA modes of action. Moreover, hmr mutants are albino in all light conditions, which suggests that HMR is required for chloroplast differentiation in the light. The albino phenotype separates hmr from all of the known photomorphogenetic mutants. Genetic studies suggest that HMR acts as a positive signal component between phytochrome and DET1, a master repressor of photomorphogenesis. The identification of HMR opens a new avenue to further unravel phytochrome early signaling networks and sets the stage to elucidate the function and regulation of phyB NBs.
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1 - The Salk Institute for Biological Studies, Plant Biology Laboratory, 10010 N. Torrey Pines Rd., La Jolla, CA, 92037, USA
2 - Howard Hughes Medical Institute, The Salk Institute for Biological Stu
Presentation Type: ASPB Minisymposium
Location: Continental C/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:55 AM