Cloning And Functional Analysis Of ?-Ketoacyl-ACP Reductase1 In Rice

Lipids are not only high energy components,but also functions as building blocks for cell membranes and are important signal molecules involved in various biological processes.Fatty acids are essential precursors for assembly of galactolipids,phospholipids and storage lipids.Loss of fatty acids will result in adverse effects on growth and development.Fatty acid synthase(FAS)is a complex consisting of multiple enzymes.?-ketoacyl-ACP reductase(KAR)is an important component in FAS complex and is a key enzyme for fatty acid biosynthesis.However,the roles of KAR in lipid metabolism and plant growth and development are still not clear in plants.In this study,KAR family was isolated from rice and Arabidopsis,and sequence analysis revealed that KARs contain conserved catalytic domain and NADPH/NADH binding domain.KAR1 was cloned from rice and the protein was expressed in E.coli cells for enzyme activity assay.The resulted showed that KAR1 is capable of catalyzing the reduction of acetoactyl-CoA by using NADPH as electron donor.KAR1 is localized to chloroplasts as shown by KAR1-GFP under laser confocal microscope.The KAR1 transcript level was relatively low in most tissues under normal growth conditions,but was rapidly induced by heat shock,low temperature,salt stress,and PEG.To further explore the role of KAR1 in lipid metabolism and growth,karl mutant was isolated and the overexpress plants were generated for functional characterization.Loss of KAR1 does not exhibit obvious phenotype under normal growth conditions,except for the reduced C18:3 FA of TAG in the seeds of mutant compared to that of wild type.However,the mutant exhibited less C18:3 FA in the leaves and was less resistant to heat shock.The results suggest that KAR1 is involved in lipid metabolism under heat shock stress conditions.