Organ fusion and defective cuticle function in a lacs1 lacs2 double mutant of Arabidopsis

As the outermost layer on aerial tissues of the primary plant body, the cuticle plays important roles in plant development and physiology. The major components of the cuticle are cutin and cuticular wax, both of which are composed primarily of fatty acid derivatives synthesized in the epidermal cells. Long-chain acyl-CoA synthetases (LACS) catalyze the formation of long-chain acyl-CoAs and the Arabidopsis genome contains a family of nine genes shown to encode LACS enzymes. LACS2 is required for cutin biosynthesis, as revealed by previous investigations on lacs2 mutants. Here, we characterize lacs1 mutants of Arabidopsis that reveals a role for LACS1 in biosynthesis of cuticular wax components. lacs1 lacs2 double-mutant plants displayed pleiotropic phenotypes including organ fusion, abnormal flower development and reduced seed set; phenotypes not found in either of the parental mutants. The leaf cuticular permeability of lacs1 lacs2 was higher than that of either lacs1 or lacs2 single mutants, as determined by measurements of chlorophyll leaching from leaves immersed in 80% ethanol, staining with toluidine blue dye and direct measurements of water loss. Furthermore, lacs1 lacs2 mutant plants are highly susceptible to drought stress. Our results indicate that a deficiency in cuticular wax synthesis and a deficiency in cutin synthesis together have compounding effects on the functional integrity of the cuticular barrier, compromising the ability of the cuticle to restrict water movement, protect against drought stress and prevent organ fusion.