Abstract
We have been working on a comparative study of abscisic acid (ABA) signaling and the function between the moss Physcomitrella patens and higher plants. Although P. patens possesses an ABA signaling pathway similar to that of higher plants, our knowledge of ABA function in the moss is limited. In this study, we generated transgenic P. patens lines that overexpress Arabidopsis CYP707A3 gene encoding an ABA 8'-hydroxylase. Because ABA 8'-hydroxylase catalyzes the first step of ABA catabolic pathway, the moss overexpressors (CYP707 OEs) were expected to accumulate less ABA. We found that the CYP707 OEs resulted in the appearance of macrochloroplasts under stress conditions. The macrochloroplast phenotype of CYP707 OEs was relieved by exogenously applied ABA, and application of an ABA biosynthesis inhibitor Abamine SG to wild type caused the macrochloroplasts phenotype. These results suggest that ABA is involved in the chloroplast division under environmental stress.
