Elucidation of mechanisms governing selectable expression of chloroplast genes and its application to plant improvement

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Gene expression in chloroplasts was selectively switched off by the modification of sigma factor 1 (SIG1). We performed genome-wide screening of Arabidopsis cDNA clones by in vitro detection of protein-protein interaction, followed by phosphorylation assay, resulting in identification of some SIG-one protein kinases (SOPKs). Under lighting conditions that preferentially excited PS I, expression profiles of the psaA gene for the reaction center protein of PS I in SOPK-knockout (KO) lines, were consistent with SIG1 being in its unphosphorylated state. Employment of GFP fused with these SOPKs revealed their localization in the cytosol. SIG-one protein phosphatase (SOPH) candidate genes were tried to be identified by similar strategies. This "light switch" was further employed for chloroplast engineering. On the other hand, "gyokuro" green tea enriched with amino acids, is made of tea leaves grown under a light-shaded condition. Such leaves were subjected to transcriptomic analysis.