Arabidopsis RADICAL-INDUCED CELL DEATH1 is involved in UV-B signaling

The Arabidopsis radical-induced cell death1 (rcd1) mutant is sensitive to ozone fumigation and apoplastic superoxide, but tolerant to methyl viologen. In the present article, we report that the rcd1 mutant is also tolerant to supplementary UV-B radiation. The rcd1-1 mutant exhibits less accumulation of TT dimers, increased hypocotyl growth inhibition and higher accumulation of flavonoids under supplemental UV-B radiation. Moreover, the expression of HY5 (ELONGATED HYPOCOTYL5) is increased in the mutant after UV-B treatment. Gene expression downstream of UV-B signaling reveals that COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC1)-regulated genes have an elevated expression in rcd1-1 mutant under UV-B radiation, while expression of UVR8 (UV RESISTANCE LOCUS 8)-regulated and HY5-independent genes are not changed. Interestingly, the expression of RCD1 genes is not significantly changed by UV-B radiation. Previous study has shown that STO protein is interacting with RCD1 in vitro. Here, we found the mRNA level of STO ( SALT TOLERANCE) is greatly increased in rcd1-1 mutant after UV-B radiation. However, UV-B-induced HY5 and CHS expression is partially inhibited in sto mutant. Based on the above results, it is deduced that the RCD1, working together with STO, is involved in Arabidopsis UV-B signaling.