| Summary: | 碩士 === 國立臺灣大學 === 分子與細胞生物學研究所 === 100 === The 70 kD heat shock proteins (Hsp70s) are involved in protein translocation, folding and degradation. We have recently shown that chloroplast Hsp70s, cpHsc70s, are involved in protein import into chloroplasts. Since the J protein cochaperones are drivers that recruit Hsp70 for specific functions, we intend to identify the J protein assisting cpHsc70s in chloroplast protein import. There are more than one hundred J proteins in Arabidopsis, and at least 19 of them are localized in chloroplasts. Among them, J25 is predicted to localize in membranes. I found that J25 has a dual localization: the majority of J25 is localized in the thylakoid membrane and a small portion is localized in the inner envelope membrane. However, the j25 mutants show no defect in the import of a model chloroplast precursor protein. Nonetheless, I found another interesting phenotype of the j25 mutants: one of the alleles has long hypocotyls when grown under white and red light and double mutants of both alleles with a phyB (phytochrome B, the major red light sensor of plants) mutant have an additive long hypocotyl phenotype under white light and red light. In addition, the j25/phyB double mutants have an additive defect in seeds germination. These data suggest that J25 is involved in light sensing and that J25 and phyB are involved in independent red light signaling pathways. Characterizations of J25 provide a possible link between chloroplast Hsp70 and light-regulated signal transduction.
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