Poster: Nutrient Biology
Abs #
396: Protein degradation under nutrient depletion in Arabidopsis -proteomics approach-
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Presenter: |
Koizumi, Nozomu , nkoizumi@gtc.aist-nara.ac.jp |
Authors | Koizumi, Nozomu (A) Deji, Atsushi (A) Sano, Hiroshi (A) | | Affiliations: |
(A): Nara Institute of Science and Technology
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Plants assimilate inorganic compounds to organic compounds with solar energy. Assimilates (such as starch and proteins) in leaves are often degraded to movable compounds (such as sugars and amino acids) and transported to other organs where they are stored. This phenomenon is marked during senescence. While the mechanism of protein degradation in this process is largely unknown, recent studies have been indicating at least three independent machinery functioning. They are degradation in chloroplasts, ubiquitin/proteosome system and vacuolar related degradation (eg. autophagy). At first we aimed to clarify how these machinerys are cooperatively organized. Thus, we observed phenomena that occurred in leaves of Arabidopsis under nitrogen or carbon depletion. Amount of total proteins and chlorophyll contents were decreased associating with the increase of ubiquitination and protease activity. We also examined expression pattern of several senescence-associated genes. Subsequently, protein profiles under this process were analyzed with two-dimensional gels. Although amount of total proteins markedly decreased, some proteins increased or remained at the same level. We are considering that some of these proteins function in degradation of proteins and then identifying dozens of such protein with mass spectrometry. One of the interesting candidates is a chloroplast localizing cyclophilin, a member of peptidyl-prolyl isomerases (PPIs). PPIs are generally considered to function for folding or refolding of proteins. Since the PPI localized to the stroma, we postulate that the PPI is involved in refolding of stroma proteins such as Rubisco and makes them accessible to proteases. Further characterization of proteins including this PPI will be reported.
