Synergistic control of chloroplast biogenesis by MYB-related and Golden2-like transcription factors

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 also 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 mutants of GLK. In M. polymorpha MYB-related genes act upstream of GLK, while in A. thaliana this relationship has been rewired. In both species, 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 the MYB-related proteins. Thus, MYB-related and GLK genes have overlapping as well as distinct targets. We conclude that together MYB-related and GLK transcription factors orchestrate chloroplast development in land plants.