Photoreceptor–induced sinapate synthesis contributes to photoprotection in Arabidopsis

Abstract

ABSTRACTPlants must balance light capture for photosynthesis with protection from potentially harmful ultraviolet radiation (UV). Photoprotection is mediated by concerted action of photoreceptors, but the underlying molecular mechanisms are not fully understood. In this study, we provide evidence that UV RESISTANCE LOCUS 8 (UVR8) UV-B-, phytochrome red-, and cryptochrome blue-light photoreceptors converge on the induction ofFERULIC ACID 5-HYDROXYLASE 1(FAH1) that encodes a key enzyme in the phenylpropanoid biosynthesis pathway, leading to the accumulation of UV-absorbing sinapate esters.FAH1induction depends on the bZIP transcription factors ELONGATED HYPOCOTYL 5 (HY5) and HY5-HOMOLOG (HYH) that function downstream of all three photoreceptors. Noticeably, mutants with hyperactive UVR8 signalling rescuefah1UV sensitivity. Targeted metabolite profiling suggests that this phenotypic rescue is due to the accumulation of UV-absorbing metabolites derived from precursors of sinapate synthesis, namely coumaroyl-glucose and feruloyl-glucose. Our genetic dissection of the phenylpropanoid pathway combined with metabolomic and physiological analyses show that both sinapate esters and flavonoids contribute to photoprotection with sinapates playing a major role for UV screening. Our findings indicate that photoreceptor-mediated regulation ofFAH1and subsequent accumulation of sinapate “sunscreen” compounds is a key protective mechanism to mitigate damage, preserving photosynthetic performance, and ensuring plant survival under UV.