Wax Crystal-Sparse Leaf1 encodes a beta-ketoacyl CoA synthase involved in biosynthesis of cuticular waxes on rice leaf

Cuticular waxes, forming the plant/atmosphere interface of plants colonizing the terrestrial environment, are complex mixtures of very-long chain fatty acids (VLC-FAs) and their derivatives. In VLCFAs biosynthesis, beta-ketoacyl CoA synthase (E.C.2.3.1.119, KCS) is the key enzyme. Using T-DNA insertional mutagenesis, we identified a cuticle-deficient rice mutant, which displayed a pleiotropic phenotype including reduced growth, leaf fusion, sparse wax crystals, enhanced sensitivity to drought and low fertility. Further analysis indicated that T-DNA was inserted in the 5'-UTR intron of the affected gene, Wax Crystal-Sparse Leaf1 (WSL1), and abnormal transcript caused the loss-of-function of WSL1 gene. Genetic complementation experiment confirmed the function of the candidate gene. WSL1 was predicted to encode a polypeptide containing a conserved FAE1_CUT1_RppA domain typical of the KCS family proteins. Qualitative and quantitative wax composition analyses by gas chromatography-mass spectrometry (GC-MS) demonstrated a marked reduction of total cuticular wax load on wsl1 leaf blades and sheaths, and VLCFA precursors of C20-C24 decreased in both. Moreover, ubiquitous expression of the WSL1 gene gave a hint that WSL1-catalyzed elongation of VLCFAs might participate in a wide range of rice growth and development processes beyond biosynthesis of cuticular waxes.