Far red light induces the expression of LHCSR to trigger nonphotochemical quenching in the intertidal green macroalgae Ulva prolifera

Plants and algae must acclimate to changes in light conditions including light intensity and light quality. Socalled nonphotochemical quenching (NPQ) is the fastest response to high light intensity and light qualifies relying on photosystem II subunit S (PSBS) and light-harvesting complex (LHC) stress-related (LHCSR). Far- red light (FRL) reaching intertidal green macroalgae changes frequently. Here, we report that FRL stimulates cyclic electron flow (CEF) around photosystem I (PSI) and enhances NPQ in Ulva prolifera (Chlorophyta). The increased de-epoxidation state indicated the participation of the xanthophyll cycle. Moreover, the expression of LHCSR, but not that of PSBS was induced and combined with LHCII trimmer when exposed to FRL. In contrast, neither PSBS nor LHCSR was overexpressed under high light irradiance compared with normal-light and dark-treated samples, which was contrast to results obtained in moss Physcomitrella patens (Bryophytes). Lhcbl and CP29 were up-regulated under FRL, implying an increased photosystem II antenna size. In conclusion, FRL can enhance CEF around PSI and induce the expression of LHCSR to trigger NPQ in U. prolifera, which may be important for its well adaption to intertidal environment.