Modulation of gene expression of carotene biosynthesis-related protein by photosynthetic electron transport for the acclimation of intertidal macroalga Ulva fasciata to hypersalinity and excess light

A gene (UfCBR) encoding carotene biosynthesis-related (CBR) protein that potentially functions for the dissipation of excessive energy has been cloned from the intertidal green macroalga Ulva fasciata Delile. Hypersalinity and high light ≥300 µmol m−2 s−1 increased both UfCBR mRNA level and non-photochemical quenching (NPQ). The increase of UfCBR mRNA level and NPQ by high light was inhibited by treatment of photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, but not by stigmatellin, an inhibitor that blocks electron transfer from quinol oxidase to iron–sulfur protein in cytochrome b6f complex. Treatment of dimethylthiourea, an H2O2 scavenger, under 1200 µmol m−2 s−1 condition inhibited H2O2 accumulation but did not affect UfCBR mRNA level, while treatment of H2O2 in 150 µmol m−2 s−1 condition decreased UfCBR mRNA level. Thus, an reactive oxygen species-independent redox control via a more reduced state downstream the cytochrome b6f complex is involved in high light up-regulation of UfCBR expression in U. fasciata. The expression of UfCBR in U. fasciata against oxidative stress occurring in high light or high salinity in relation to NPQ is discussed.