UV RESISTANCE LOCUS 8 (UVR8) is an ultraviolet-B (UVB) radiation photoreceptor that mediates light responses in plants. How plant UVR8 acts in response to UVB light is not well understood. Here, we report the identification and characterization of the Arabidopsis WRKY DNA-BINDING PROTEIN 36 (WRKY36) protein. WRKY36 interacts with UVR8 in yeast and Arabidopsis cells and it promotes hypocotyl elongation by inhibiting HY5 transcription. Inhibition of hypocotyl elongation under UVB requires the inhibition of WRKY36. WRKY36 binds to the W-box motif of the HY5 promoter to inhibit its transcription, while nuclear localized UVR8 directly interacts with WRKY36 to inhibit WRKY36–DNA binding both in vitro and in vivo, leading to the release of inhibition of HY5 transcription. These results indicate that WRKY36 is a negative regulator of HY5 and that UVB represses WRKY36 via UVR8 to promote the transcription of HY5 and photomorphogenesis. The UVR8–WRKY36 interaction in the nucleus represents a novel mechanism of early UVR8 signal transduction in Arabidopsis.
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We thank X. Huang, Y. Shi, R. P. Hellens and Q. Hu for materials and technical assistance. We thank G. A. Gomez for copyediting the manuscript. This work is supported in part by the National Key Research and Development Program of China (2017YFA 0503800), National Natural Science Foundation of China (31730009, 31721001, 31670282 and 31670307) and Strategic Priority Research Program ‘Molecular Mechanism of Plant Growth and Development’ (XDPB04).
The authors declare no competing financial interests.
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