KCS4 stands at a major junction of abiotic-stress-induced lipid rearrangement in Arabidopsis

LUZAROWSKA U; LUZAROWSKI M; CORREAS CORDOBA; THIRUMALAI KUMAR V. P; CUADROS-INOSTROZA A.; WU S.; SCHUMACHER J.; ZHU F.; FERNIE A. R.; FUSARI CM; BROTMAN Y

Marseille

Simposio; 9th European Symposium on Plant Lipids; 2019

Deutsche Gesellschaft für Fettwissenschaft e.V.

Although genes encoding proteins responsible for lipid biosynthesis and regulation have been extensively studied in A. thaliana, our knowledge about their genetic basis is not complete. From the currently 700 putatively annotated lipid-metabolism genes, the function of only ~40% is biochemically or genetically proven. We exposed a panel of 314 A. thaliana accessions to a combined stress of heat and darkness. Lipids were extracted from rosette leaves, quantified using LC?MS, and subjected to a genome-wide association study (GWAS), using lipid levels as quantitative traits. The quantitative trait locus (QTL) harboring the 3-ketoacyl-CoA synthase 4 (KCS4) gene was strongly associated with 26 highly polyunsaturated triacylglycerols (TAGs; LOD ≥ 13 for all mapped TAGs), but was not detected in the control-condition GWAS. KCS4, with 21 members in Arabidopsis, is the first enzyme of the elongase complex, which mediates synthesis of very long chain fatty acids (VLCFA), by incremental elongation of the chain. KCS is also the rate-limiting and specificity-determining component of the complex. KCS4?s closest homologues are: KCS9, involved in the elongation of C22 fatty acids to C24; KCS17, which has not yet been characterized; and KCS18, the first characterized KCS enzyme, involved in elongating acyl‐CoAs to C20, C20:1, and C22:1 in seeds and shown to drive the natural variation in the abundance of VLCFAs in this organ. As for KCS4, its specificity and function remain unknown. Polyunsaturated fatty acids are known to release from the membrane upon stress, and to cause oxidative damage to cell components. Often, however, cell mechanisms manage to sequester these fatty acids in TAGs, thereby exerting protection against this so-called lipotoxicity. The effect of KCS4 on the sequestration of polyunsaturated fatty acids into TAGs under abiotic stress indicates that KCS4 stands at a major junction in lipid metabolism, and the extreme variation in the natural abundance of the KCS4 may provide insights with regards to plant response mechanisms to abiotic stress and to the adaptive selection pressures that shape them.