Abstract
To better understand the mechanism of phytochrome-mediated signaling, we used a basal land plant, the liverwort Marchantia polymorpha L.. Phytochrome in M. polymorpha, Mpphy, is encoded by a single-copied gene, MpPHY. Mpphy exhibits red/far-red photoreversibility in vitro, which is lost in Mpphy with a single amino-acid substitution, MpphyY241H. Mpphy has been shown to promote cell division after spore germination, development to thallus, and thallus regeneration. In this study, chromosomes were visualized by tdTomato fused with histone H2B, which revealed that meristem formation and cell division are red-light dependent. Comparison of nuclear phase between transgenic plants carrying MpphyY241H and WT implied that Mpphy could facilitate transition from G2 phase to M phase. Mpphy was largely localized in the nucleus after red-light irradiation, while MpphyY241H was detected in the nucleus as well as in the cytoplasm regardless of light condition. Silencing of MpPHY by RNAi caused transition into reproductive phase without far-red light. These results indicate that Mpphy is functional in the nucleus, and also that Mpphy regulates morphogenesis directly or indirectly by cell division.
