Arabidopsis 3-Ketoacyl-CoA Synthase 4 is Essential for Root and Pollen Tube Growth

Very long-chain fatty acids (VLCFAs) are essential precursors of membrane lipids, such as phospholipids and sphingolipids, cuticular waxes, suberins, and Brassica seed oils. The first step of VLCFA synthesis is mediated by 3-ketoacyl-CoA synthase (KCS), which catalyzes the condensation of a C2 unit from malonyl-CoA to acyl-CoA. In the present study, we investigated the role of KCS4 in pollen tube and root growth. KCS4 was predominantly expressed in shoot and root apical meristems, leaf veins, mature and germinated pollen grains, and developing embryos. The fluorescent signals of KCS4 fused with enhanced yellow fluorescent protein (KCS4:eYFP) were detected in the endoplasmic reticulum of tobacco epidermis. KCS4 disruption inhibited pollen tube elongation and root growth, whereas KCS4 promoter-driven KCS4 expression rescued the growth-retarded phenotype to wild type (WT) in kcs4 complementation lines. Root growth assay of WT and kcs4 lines treated with metazachlor and mefluidide, which are specific KCS inhibitors, and fatty acid analysis of their roots and seeds revealed that KCS4 is involved in the elongation of longer than C24 VLCFAs, which are essential for root and pollen tube growth.