Abstract
Chloroplast has developed the sophisticated translation system using only 30 tRNAs that correspond to all 20 amino acids. Researches of sigma factors of eubacteria-type plastid encoded RNA polymerase (PEP) suggest that transcription of some tRNAs including tRNA-Glu, which is essential for tetrapyrrole synthesis, is regulated by SIG2 and SIG6 during chloroplast development. In this study, we investigated the extended dynamism of chloroplasts tRNA expression in response to environmental condition. In the dark condition photosynthetic mRNAs were surely decreased, whereas chloroplast tRNAs were accumulated inversely. This phenomenon was observed even in SIG2 or NEP deficient mutants. Similar accumulation was occurred by change of N/C balance in medium or by addition of chloroplast translation inhibitors. Overexpression of the plastid glutamyl-tRNA synthetase, however, did not affect the accumulation. Based on these results, we will discuss physiological meaning and molecular mechanism of the unique dynamism.
