De Novo Biosynthesis of Fatty Acids is Important for Maintenance of Photochemical Activity under Low Temperature Environments in Arabidopsis

Abstract

The Arabidopsis thaliana kas3 mutant was isolated based on its hypersensitivity of photosystem (PS) II to low temperature using a chlorophyll (Chl) fluorescence imaging system. Chl content was lower in kas3 seedlings cultured at 23 °C than in the wild type, but maximum PSII activity was only mildly affected. We also clarified that the activity and levels of photosynthetic electron transport machinery were reduced after chilling treatment. The kas3 mutation causes an amino acid alteration in 3-ketoacyl-ACP synthase III (KasIII) which catalyzes the first decarboxy condensation step in de novo fatty biosynthesis in plastids. The defect in KasIII led to the partial loss of the de novo synthesis pathway for fatty acids in plastids. Consequently, the total fatty acid level was reduced to 75% of the wild-type level in kas3 at 23 °C and was further reduced to 60% at 4 °C. The full activity of KasIII is required for the biogenesis of intact photosynthetic machinery in thylakoid membranes and is especially important for the process responding to low temperature.