Transcription factors BBX11 and HY5 interdependently regulate the molecular and metabolic responses to UV-B

UV-B radiation acts as a developmental cue and a stress factor for plants, depending on dose. Activation of the transcription factor ELONGATED HYPOCOTYL 5 (HY5) in a UV RESISTANCE LOCUS 8 (UVR8)-dependent manner leads to the induction of a broad set of genes under UV-B. However, the underlying molecular mechanisms regulating this process are less understood. Here, we use molecular, biochemical, genetic, and metabolomic tools to identify the B-BOX transcription factor BBOX PROTEIN 11 (BBX11) as a component of the molecular response to UV-B in Arabidopsis (Arabidopsis thaliana). B-BX11 expression is induced by UV-B in a dose-dependent manner. Under low UV-B, BBX11 regulates hypocotyl growth suppression, whereas it protects plants exposed to high UV-B radiation by promoting the accumulation of photo-protective phenolics and antioxidants, and inducing DNA repair genes. Our genetic studies indicate that BBX11 regulates hypocotyl elongation under UV-B partially dependent on HY5. Overexpression of BBX11 can partially rescue the high UV-B sensitivity of hy5, suggesting that HY5-mediated UV-B stress tolerance is partially dependent on BBX11. HY5 regulates the UV-B-mediated induction of BBX11 by directly binding to its promoter. BBX11 reciprocally regulates the mRNA and protein levels of HY5. We report here the role of a B-BX11-HY5 feedback loop in regulating photomorphogenesis and stress tolerance under UV-B.

Automated summary

UV-B radiation has dual effects on plants, acting as a developmental cue or a stress factor depending on dosage. The B-BOX transcription factor BBX11 plays a crucial role in the molecular response to UV-B, regulating hypocotyl growth and protecting plants from high UV-B radiation by promoting the accumulation of photo-protective compounds and inducing DNA repair genes. BBX11 and the transcription factor HY5 mutually regulate each other, contributing to UV-B-mediated photomorphogenesis and stress tolerance.