Streamlined regulation of chloroplast development in the liverwortMarchantia polymorpha

AbstractPhotosynthesis in eukaryotic cells takes place in specialised plastids. The regulation of plastid development is crucial for multicellular systems such as plants. Two families of transcription factors known as Golden2-like (GLK) and GATA regulate plant chloroplast development, and the miR171-targeted SCARECROW-LIKE (SCL) GRAS transcription factors regulate chlorophyll biosynthesis. The extent to which these proteins carry out conserved roles in non-seed plants such as the liverworts is not known. Here we determine the degree of functional conservation of the GLK, GATA and SCL proteins in controlling chloroplast development in the model liverwortMarchantia polymorpha. Our results indicate that GATA and SCL do not play a detectable role in chloroplast biogenesis but loss of GLK function leads to reduced chloroplast size, underdeveloped thylakoid membranes and lower chlorophyll accumulation. These findings suggest that the functioning of GATA and SCL in chloroplast development either evolved after the divergence of vascular plants from bryophytes, that both roles were secondarily lost inM. polymorpha, or that functional redundancy is masking their roles. In contrast, and consistent with its presence in algae, GLK plays a conserved role in chloroplast biogenesis of liverworts and vascular plants.