BBX10 interacts with PIF1 to prevent photo-oxidation and to promote the greening process

Seedlings emerged from the covering soil immediately undergo de-etiolation, ensuring plants switch from heterotrophic to photoautotrophic growth. This transition is essential for seedling development and survival. However, the underlying mechanism remains largely obscure. Here, we identified that B-box PROTEIN 10 (BBX10) inhibits the biosynthesis of protochlorophyllide in darkness and accumulation of reactive oxygen species (ROS) upon light exposure, hence leading to the increase of seedling greening and survival during de-etiolation. BBX10 interacts with PHYTOCHROME INTERACTING FACTOR 1 (PIF1) and enhances its DNA-binding affinity and transcriptional repression or activation activity toward target genes GENOMES UNCOUPLED 5 (GUN5) and ASCORBATE PEROXIDASE 2 (APX2), respectively. Genetically, BBX10 acts upstream of PIF1, GUN5, and APX2 in regulating of greening. Together, our study reveals that the BBX10-PIF1 transcriptional module inhibits the protochlorophyllide biosynthesis in darkness and ROS accumulation upon light irradiation, through which seedlings protect themselves against photo-oxidative damage upon emerging from the soil.