Poster: Photosynthesis
Abs #
355: Regulation of Fd-GOGAT gene expression for maintaining balance between Carbon and nitrogen Photoassimilations in cyanobacterium Plectonema boryanum
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Presenter: |
Shinmura, Kanako , kanako@protein.osaka-u.ac.jp |
Authors | Shinmura, Kanako (A) Okuhara, Hiroaki (A) Toshiharu, Hase (A) | | Affiliations: |
(A): Institute for Protein Research Osaka University
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Two different types of glutamate synthase (GOGAT) are present in Plectonema boryanum: one requires Fd and the other NADH as an electron donor. Analyses of mutants deficient in each gene have indicated that Fd-GOGAT has a major role in maintaining the balance of N and C photoassimilation. In this study we analyzed the physiological role of GOGAT in balancing C and N metabolism in this cyanobacterium, and regulation of its gene expression by C and N status. 1) Homeostasis in the cellular content of amino acids was well maintained in wild type and NADH-GOGAT mutant cells irrespective of culture conditions. In the Fd-GOGAT mutant, however, a remarkable accumulation of Gln was observed during active C assimilation. 2) Fd-GOGAT protein content of the wild type increased about 2-fold in response to the active C assimilation. 3) When the Fd-GOGAT mutant was complemented with the Fd-GOGAT gene, its N assimilation capacity was restored, but when transformed with NADH-GOGAT gene, its phenotype remained N deficient, due to the absence of Fd-GOGAT. 4) The Fd-GOGAT gene promoter had a rapid up- and down- regulation in response to changes in C-assimilation capacity.
Our results suggest that Fd-GOGAT is located at a regulatory points in the coordination of N and C assimilation; the increase of Fd-GOGAT protein level, when C-assimilation capacity is elevated, is crucial for balancing N-/C-assimilation and NADH-GOGAT is unable to act as substitute for Fd-GOGAT. Additionally, a novel fact found by our study was that the Fd-GOGAT gene is controlled by C assimilation capacity at the transcriptional level and the cellular pool of Gln may contribute to this signaling pathway.
