BBX24 Interacts with DELLA to Regulate UV-B-Induced Photomorphogenesis in Arabidopsis thaliana

Abstract

s: UV-B radiation, sensed by the photoreceptor UVR8, induces signal transduction for plant photomorphogenesis. UV-B radiation affects the concentration of the endogenous plant hormone gibberellin (GA), which in turn triggers DELLA protein degradation through the 26S proteasome pathway. DELLA is a negative regulator in GA signaling, partially relieving the inhibition of hypo-cotyl growth induced by UV-B in Arabidopsis thaliana. However, GAs do usually not work inde-pendently but integrate in complex networks linking to other plant hormones and responses to ex-ternal environmental signals. Until now, our understanding of the regulatory network underlying GA-involved UV-B photomorphogenesis had remained elusive. In the present research, we inves-tigate the crosstalk between the GA and UV-B signaling pathways in UV-B-induced photomorpho-genesis of Arabidopsis thaliana. Compared with wild type Landsberg erecta (Ler), the abundance of HY5, CHS, FLS, and UF3GT were found to be down-regulated in rga-24 and gai-t6 mutants under UV-B radiation, indicating that DELLA is a positive regulator in UV-B-induced photomorphogen-esis. Our results indicate that BBX24 interacts with RGA (one of the functional DELLA family mem-bers). Furthermore, we also found that RGA interacts with HY5 (the master regulator in plant pho-tomorphogenesis). Collectively, our findings suggest that the HY5–BBX24–DELLA module serves as an important signal regulating network, in which GA is involved in UV-B signaling to regulate hypocotyl inhibition.