Light is an important environmental cue and regulates plant development
processes including de-etiolation, phototropism, shade avoidance, photoperiodic
flowering, stomatal movement and so on. In Chapter II, we reported cloning of an
Arabidopsis light-signaling component, HYPOSENSITIVE TO LIGHT or HTL. htl
mutants displayed a long hypocotyl phenotype under red, far-red, and blue light, as well
as other photomorphogenic defects. HTL belongs to an alpha/beta fold protein family and
is localized predominantly in the nucleus. ELONGATED HYPOCOTYL5 (HY5), a BZip
transcription factor, directly binds to both C/G-box and G-box in HTL promoter and
regulates HTL expression. Evidences suggest that HTL represents a new signaling step
downstream of HY5 in de-etiolation responses. In Chapter III, we discovered the role of
HYPERSENSITIVE TO RED AND BLUE1 (HRB1) and PHOSPHATE7 (PP7) in lightinduced
stomatal movement response. Besides its short hypocotyl phenotype upon
isolation, hrb1 mutant also showed reduced water loss and stomatal aperture phenotypes
under blue light. We identified PP7 as an HRB1 interacting protein. PP7 dephosphorylated
HRB1 in vivo and HRB1 required a functional PP7 for both its stomatal opening and hypocotyl elongation responses. HRB1 was found in a protein complex of
193 kDa in the dark and blue light induced a size shift to 285 kDa. However, the size
shift of HRB1 protein complex was largely impaired and HRB1 was predominately
phosphorylated in pp7 mutant. We propose that a modification of HRB1 by PP7 under
blue light is essential to acquire a proper conformation of the HRB1 protein complex or
to bring in a new component for the assembly of a functional HRB1 protein complex.
University of Minnesota Ph.D. dissertation. August 2011. Major: Plant Biological Sciences. Advisor: Dr. Min Ni. 1 computer file (PDF); viii, 106 pages.
Regulation of de-etiolation and stomatal opening responses by HYPOSENSITIVE TO LIGHT and HYPERSENSITIVE TO RED AND BLUE 1..
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