|Schnurr, Judy - UNIVERSITY OF MINNESOTA|
|Browse, John - WASHINGTON STATE UNIV.|
Submitted to: The Plant Cell
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 27, 2003
Publication Date: March 1, 2004
Citation: Schnurr, J., Shockey, J.M., Browse, J. 2004. The acyl-coenzyme a synthetase encoded by lacs2 is essential for normal cuticle development in arabidopsis. The Plant Cell. 16:629-642. Interpretive Summary: Long-chain acyl-CoA synthetase (LACS) activities are encoded by a family of at least nine genes in Arabidopsis (Arabidopsis thaliana). These enzymes have roles in lipid synthesis, fatty acid catabolism, and the transport of fatty acids between subcellular compartments. Here, we show that the LACS2 gene (At1g49430) is expressed in young, rapidly expanding tissues, and in leaves expression is limited to cells of the adaxial and abaxial epidermal layers, suggesting that the LACS2 enzyme may act in the synthesis of cutin or cuticular waxes. A lacs2 null mutant was isolated by reverse genetics. Leaves of mutant plants supported pollen germination and released chlorophyll faster than wild-type leaves when immersed in 80% ethanol, indicating a defect in the cuticular barrier. The composition of surface waxes extracted from lacs2 leaves was similar to the wild type, and the total wax load was higher than the wild type (111.4 µg/dm2 versus 76.4 µg/dm2, respectively). However, the thickness of the cutin layer on the abaxial surface of lacs2 leaves was only 22.3 ± 1.7 nm compared with 33.0 ± 2.0 nm for the wild type. In vitro assays showed that 16-hydroxypalmitate was an excellent substrate for recombinant LACS2 enzyme. We conclude that the LACS2 isozyme catalyzes the synthesis of -hydroxy fatty acyl-CoA intermediates in the pathway to cutin synthesis. The lacs2 phenotype, like the phenotypes of some other cutin mutants, is very pleiotropic, causing reduced leaf size and plant growth, reduced seed production, and lower rates of seedling germination and establishment. The LACS2 gene and the corresponding lacs2 mutant will help in future studies of the cutin synthesis pathway and in understanding the consequences of reduced cutin production on many aspects of plant biology.
Technical Abstract: The above-ground parts of all land plants are covered by a waxy coating called the cuticle. The cuticle contains a complex mixture of lipid molecules derived from fatty acids that are originally produced inside the cells of the plant. Until recently, very little was known about the numbers and types of enzymes that were needed to produce the cuticle precursor lipids. This study focused on the characterization of a mutant form of the plant Arabidopsis thaliana that contained an defective cuticle layer on its leaves. The cuticle defect was traced to a defect in the gene LACS2. LACS2 is one of nine known Arabidopsis LACS genes, all of which produce enzymes called long chain acyl-CoA synthetases. These enzymes activate fatty acids by converting them to compounds called acyl-CoAs. Acyl-CoAs were previously thought to serve as building blocks for the cuticle layer, but it had not been proven. The most important finding in this paper was the demonstration that the defect in LACS2 clearly established a functional link between acyl-CoA synthesis and cuticle synthesis. These findings will be very helpful to plant scientists interested in acyl-CoA and lipid metabolism. The mutant Arabidopsis plant will also serve as a powerful tool for scientists who seek to understand and manipulate the cuticle layer of plants.