OsUVR8b, rather than OsUVR8a, plays a predominant role in rice UVR8-mediated UV-B response.
UV RESISTANCE LOCUS 8 (UVR8) has been identified in Arabidopsis thaliana as the receptor for UV-B radiation mediating photomorphogenic responses and acclimation to UV-B radiation. However, UVR8-mediated UV-B signaling pathways in rice, that has two proteins (UVR8a and UVR8b) with homology to AtUVR8, remain largely unknown. In this study, UVR8a and UVR8b were found to be expressed mainly in rice leaves and leaf sheaths, while the level of UVR8b was higher than that of UVR8a. In agreement with prior studies on AtUVR8, uvr8b and uvr8a uvr8b rice mutants exposed to UV-B showed reduced UVB-induced growth inhibition and upregulation of CHS and HY5 transcripts along with acclimation to UV-B, overexpressing UVR8a or UVR8b enhanced UV-B-induced growth inhibition and acclimation to UV-B, compared to wild-type plants. UV-B was able to enhance the interaction between CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1) with UVR8a/UVR8b, whereas the interaction intensity of REPRESSOR OF UV-B PHOTOMORPHOGENESIS2 (RUP2) with UVR8a was significantly higher than that with UVR8b. In addition, UVR8a and UVR8b were also found in the nucleus and cytoplasm, but OsUVR8 proteins were localized in nucleus in the absence of UV-B. The level of OsUVR8 monomer showed an invisible change in the leaves of rice seedlings transferred from white light to white light supplemented with UV-B, even UV-B can weaken the interactions of UVR8a or/and UVR8b. Therefore, both UVR8a and UVR8b, that have different location and response modes with Arabidopsis UVR8, function in the response of rice to UV-B radiation, whereas UVR8b plays a predominant role in this process.