Browsing by Subject "Photomorphogenesis"
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Item A role for UV-B -induced DNA damage in photomorphogenic responses in etiolated Arabidopsis seedlings(2014-01) Biever, Jessica JoUltraviolet (UV) radiation is a constituent of sunlight that influences plant morphology and growth. It induces photomorphogenic responses but also causes damage to DNA. Plant responses to DNA damage caused by UV-B light are often categorized as general mechanisms that get activated by other environmental stresses. Photodimers are formed through the direct absorption of UV-B light by DNA and are removed, in part, by nucleotide excision repair (NER). UV-B irradiation resulted in the accumulation of the two most common photodimers, cyclobutane pyrimidine dimers (CPDs) and pyrimidine-(6,4)-pyrimidinone dimers (6,4PPs), in etiolated wild type (wt) Arabidopsis seedlings. Arabidopsis mutants of the endonucleases that function in NER, xpf-3 and uvr1-1, show hypersensitivity to UV-B (280-320 nm) in terms of hypocotyl growth inhibition. I hypothesized that the accumulation of UV-B-induced photodimers was responsible for the hypocotyl growth phenotype of these NER mutants after UV-B irradiation. It was also predicted that the accumulation of photodimers could ultimately trigger signaling pathways that result in cell-cycle arrest through stalled replication sites or double-strand breaks. This was tested using the suppressor of gamma 1 (sog1-1) mutant, which lacks a transcription factor responsible for gene induction and cell-cycle arrest after gamma irradiation, and a Col-0 line containing a CYCB1;1-GUS reporter construct. CYCB1;1 encodes a cyclin that accumulates in response to cell-cycle arrest at the G2/M transition. The main conclusion from this work is that hypocotyl growth inhibition induced by UV-B light in etiolated Arabidopsis seedlings, which is a classic photomorphogenic response, is influenced by signals originating from UV-B light absorption by DNA that lead to cell-cycle arrest. Furthermore, this process is shown to occur independently of UVR8 and its signaling pathway responsible for CHS induction. This work also demonstrates that UV-B-induced DNA damage can be responsible for specific photomorphogenic responses, at least in etiolated Arabidopsis seedlings, and does not simply induce general stress responses.Item The role of SHORT HYPOCOTYL UNDER BLUE 1 in Arabidopsis seed and seedling development.(2010-01) Zhou, YunSHORT HYPOCOTYL UNDER BLUE 1 or SHB1 was previously identified as a negative regulator of the cryptochrome-mediated blue light response in Arabidopsis early seedling development. shb1, a T-DNA insertional loss-of-function allele, showed a short hypocotyl phenotype only under blue light, whereas shb1-D, a gain-of-function over-expression allele, showed a long hypocotyl phenotype under blue as well as red or far red light. SHB1 is a nuclear protein and contains a N-terminal SPX domain and a C-terminal EXS homologous to yeast SYG1 protein family. Using a biochemical approach, I found that SHB1 is anchored to a large protein complex through both of its SPX and EXS domains. In a genetic screen, I identified five mis-sense mutations within or nearby its N-terminal SPX domain and these mutation impaired its biological function and proper assembly into a protein complex. In contrast, the C-terminal EXS domain, when over-expressed, created a dominant negative phenotype and interfered with the assembly of the endogenous SHB1 into a native protein complex. SHB1 also functions in flowering timing control and this involvement is likely related to its light signaling activity. In addition, SHB1 plays a specific role in a quite different developmental phase, seed development. SHB1 regulates the timing of endosperm cellularization and promotes the subsequent embryo development through its control over both cell division and cell expansion. SHB1 associates with the promoters of MINISEED3 (MINI3), a WRKY transcription factor gene, and HAIKU2 (IKU2), an LRR receptor kinase gene in vivo, and activates the expression of these two genes required for endosperm development. In summary, SHB1 plays a novel signaling role in both Arabidopsis seed and early seedling development, and this conserved function may be implicated for some SHB1-like proteins in many other organisms.