Dr. Judith Brusslan (Biological Sciences)
B.A. Biology, Middlebury College (1982)
Ph.D. Genetics, University of Chicago (1988)
As plants grow, older leaves turn yellow or senesce. Many nutrients in these leaves, including nitrogen, are then transported to the growing portions of the plant. Most of the nitrogen in leaves is present in the photosynthetic chloroplasts, and thus the breakdown of chloroplast proteins during senescence is important for the nitrogen economy of the plant. The Brusslan lab has taken a bioinformatics/genetics approach towards identifying proteases that might be involved in chloroplast protein degradation during leaf senescence. Bioinformatics tools were used to identify 18 genes encoding chloroplast proteases that displayed up-regulation of mRNA levels during senescence. A three-pronged approach has been taken to analyze the function of these genes: 1) protease::GFP fusions are being expressed in plants to confirm intracellular localization, 2) real time quantitative PCR is being used to measure protease gene mRNA levels during senescence, and 3) T-DNA insertion mutants in all protease genes have been isolated, and chloroplast protein degradation during senescence is currently being evaluated. Our early results show that at least two of the protease mutants have increased levels of RUBISCO large subunit (a chloroplast protein) at the mid point of senescence, suggesting that our approach is likely to identify proteases that participate in chloroplast protein degradation during senescence. Proteases identified by our work will be used to produce double mutants and also will be expressed at high levels to further delineate their role in chloroplast protein degradation.
Evans, IM, Rus, AM, Belanger,EM, Kimoto, M and Brusslan, JA (2009) Dismantling of Arabidopsis thaliana Mesophyll Cell Chloroplasts During Natural Leaf Senescence. Plant Biology, In Press
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