MYB-related transcription factors control chloroplast biogenesis

Chloroplast biogenesis is dependent on master regulators from the GOLDEN2-LIKE (GLK) family of transcription factors, but glk mutants contain residual chlorophyll and therefore other proteins must be involved. Here we identify MYB-related transcription factors as regulators of chloroplast biogenesis in the liverwort Marchantia polymorpha and angiosperm Arabidopsis thaliana. In both species double mutant alleles in MYB-related genes show very limited chloroplast development, and photosynthesis gene expression is perturbed to a greater extent than in GLK mutants. Genes encoding enzymes of chlorophyll biosynthesis are controlled by MYB-related and GLK proteins whilst those allowing CO2 fixation, photorespiration and photosystem assembly and repair require MYB-related proteins. Regulation between the MYB-related and GLK transcription factors appears more extensive in A. thaliana than M. polymorpha. Thus, MYB-related and GLK genes have overlapping as well as distinct targets. We conclude that MYB-related and GLK transcription factors orchestrate chloroplast development in land plants.