Molecular Mechanism Of Arabidopsis Atypical Kinase ABC1K1 Involved In Red-light Mediated Development

Light is one of the most important environmental factors for the morphogenesis of plants and light signaling networks have been extensively studied in Arabidopsis thaliana. Here, we report the characterization of Arabidopsis bleaching and dwarf in red light 1(BDR1-1) locus, loss-of-function mutations in which exhibited shorter hypocotyls and albino cotyledons under continuous red light. Adult bdr1 mutant plants grown under white light are severely dwarf and red light illumination at seedling stage enhances the dwarf phenotype of bdr1 adult plants on soil. BDR1 was identified previously as ABC1K1, a plastoglobule localized ABC1 kinase involved in chlorophyll degradation and photooxidative stress response. BDR1 is specifically expressed in cotyledon and vasculature under various light conditions and BDR1 protein localizes in plastids. Furthermore, genetic analysis indicates that bdr1 almost completely suppressed the long hypocotyls of phyB and hy5. Taken together, Arabidopsis BDR1 functions as a negative regulator in red light-mediated plant development.To identify additional components required for auto bleaching pathways activated in bdr1-2, we performed a genetic screening to find mutations which suppress the bleaching and dwarf phenotype of bdr1-2 in red light condition. Mutants that have green cotyledons in red light and can grow to big plant size as WT after planting on soil were identified in the M2 population of ethyl methanesulfonate(EMS)-mutagenized bdr1-2 mutant. rbd1-1, a mutant obtained from this screening, rescued the albino and dwarf phenotype of bdr1-1 and bdr1-2 observed in constitutive red light. RBD1 encodes another ABC1 kinase(ABC1K3) whose overexpression leads to similar phenotypic effects as observed in bdr1 mutants. RBD1 specifically localizes in the photo-damaged chloroplasts caused by continuous red light exposure and this young retroposed gene derived from a recent retrotranspositions has evolved novel functions in photoprotection. Taken together, our data demonstrate that BDR1 and RBD1 act coordinately to regulate the inner state of chloroplasts and thus uncover a new layer of regulation in plants adapting to the light environments.