Functional Study Of AtBBX21 In UV-B-Induced Photomorphogenesis In Arabidopsis

Light Is a critical environmental factor that regulates a number of developmental and physiological processes of living organisms.Besides providing the ultimate source of biological energy,light is an informational signal that regulates key developmental processes throughout the plant life cycle.Perception of light is the initial and decisive step in light signaling transduction,and it is achieved by several groups of photosensory receptor proteins.The phytochromes respond primarily to the red(R)and far red(FR)light,cryptochromes and phototropins perceive blue and ultraviolet(UV)-A light.UV RESISTANCE LOCUS 8(UVR8)perceives UV-B light.Long-wavelength and low-fluence UV-B induces plant photomorphogen i c development that is physically characterized by the inhibition of hypocotyl elongation,flavonoid accumulation,and UV-B acclimation.BBX proteins act as key factors for the regulation of seedling photomorphogenesis.SALT TOLERANCE HOMOLOG2(STH2/BBX21),which contains two B-box domain in tandem at the N terminus,has been previously demonstrated as a positive regulator of seedling photomorphogenesis in blue,red and far-red light.However.whether BBX21 is involved in UV-B-induced photomorphogenesis remains elusive.In this study,we report that BBX21 acts as a positive regulator in UV-B-induced photomorphogenesis at seedling stage.BBX21-mediated regulation of UV-B-induced photomorphogenesis is dependent on UVR8 and CONSTITUTIVELY PHOTOMORPHOGENIC1(COP1).Moreover,we show that BBX21 positively regulates the expression of COP1 and ELONGATED HYPOCOTYL5(HY5)to promote UV-B-induced photomorphogenesis.Taken together,our data suggest that BBX21 acts as a positive factor in UV-B-induced photomorphogenesis.