Streamlined regulation of chloroplast development in the liverwort Marchantia polymorpha

Abstract

Photosynthesis in eukaryotic cells takes place in chloroplasts that develop from undifferentiated plastids in response to light. In angiosperms, after perception of light de-repression allows Elongated Hypocotyl 5 (HY5) transcription factor to initiate photomorphogenesis, and two families of transcription factors known as Golden2-like (GLK) and GATA are considered master regulators of chloroplast development. The MIR171-targeted SCARECROW-LIKE (SCL) GRAS transcription factors also impact on chlorophyll biosynthesis. The extent to which these proteins carry out conserved roles in non-seed plants is not known. Here we report in the model liverwort Marchantia polymorpha that GLK controls chloroplast biogenesis and HY5 shows a small conditional effect on chlorophyll content. In contrast, GATA and SCL have no detectable roles in this fundamental process. ChIP-SEQ and RNA-SEQ revealed that MpGLK regulates many photosynthetic and chloroplast development-related genes, but also has a broader set of targets than previously reported in angiosperms. This implies GLK carries out a conserved role relating to chloroplast biogenesis in land plants but also supports extensive divergence between its targets in M. polymorpha and flowering plants. The data support the hypothesis that regulation of chloroplast biogenesis in M. polymorpha is streamlined compared with angiosperms and allows us to present a core regulatory network for chloroplast biogenesis in land plants.