NtEREBP1-NtWRKY6a-NtPAL3 module enhances plant resistance to UV-B by promoting the accumulation of flavonoids in Nicotiana tabacum.

UV-B radiation has been shown to promote ethylene release in plants, however, the roles of ethylene signal in regulating plant resistance to UV-B has been rarely studied. Here, we showed that UV-B enhances ethylene production and the expression of an ethylene-induced transcription factor gene NtEREBP1. NtEREBP1 directly binds to the GCC-box present in the promoter of NtWRKY6a to induce its expression in response to UV-B. Over-expression of NtWRKY6a enhances plant resistance to UV-B, whereas the ntwrky6a mutant exhibits increased sensitivity to UV-B stress compared to the WT control. Metabolome and transcriptome analysis revealed that the accumulation and gene expression levels of flavonoids biosynthesis pathway significantly increased in the NtWRKY6a-OE lines compared with WT. We further demonstrated NtWRKY6a directly binds to the NtPAL3 promoter, leading to its transcription activation and subsequently enhancing flavonoids synthesis. Moreover, knock-out of NtPAL3 in the NtWRKY6a-OE background significantly increased plant sensitivity to UV-B, but exogenous application of flavonoids made NtWRKY6a-OE/ntpal3 show the same UV-B resistance with NtWRKY6a-OE plants, suggesting that the flavonoids accumulation induced by NtWRKY6a-NtPAL3 contributed to plant resistance to UV-B. Taken together, our results demonstrate the roles of NtEREBP1-NtWRKY6a-NtPAL3 module in improving plant resistance to UV-B by inducing the accumulation of flavonoids.