Location: Plant Physiology and Genetics ResearchTitle: Arabidopsis ECERIFERUM9 involvement in cuticle formation and maintenance of plant water status Author
|Des Marais, David|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2012
Publication Date: 7/1/2012
Citation: Lu, S., Zhao, H., Des Marais, D.L., Parsons, E.P., Wen, X., Xu, X., Bangarusamy, D.K., Wang, G., Rowland, O., Juenger, T., Bressan, R.A., Jenks, M.A., 2012. Arabidopsis ECERIFERUM9 involvement in cuticle formation and maintenance of plant water status. Plant Physiology, Vol. 159, pp. 930-944. Interpretive Summary: Many plant genes associated with cuticle lipid synthesis have been isolated using mutagenesis approaches, and these mutation induced cuticle deficiencies cause the mutant plants to be unaffected by, or else more susceptible, to water deficiency in the growing medium. In this study, we identify a gene associated with cuticle lipid synthesis designated ECERIFERUM9 (CER9), whose mutation causes improved tolerance to water deficiency, improved water use efficiency, and lower transpiration rates. Among other altered cuticle characters, cer9 has a thicker cuticle membrane (a structure determined primarily by the cutin polyester) and higher amounts of total cutin monomers. CER9 encodes a predicted E3 ubiquitin ligase, potentially involved in targeting cuticle lipid associated proteins for degradation. The cer9 mutation causes changes in the level of expression of other genes, having its primary effect on stress-related genes, rather than lipid metabolism genes, as was anticipated. The CER9 gene product appears to serve as a targeted regulator in the synthesis of cuticle lipids associated with drought stress tolerance traits, and as such, may be useful in the development of novel genetic strategies for improving drought tolerance in crop plants.
Technical Abstract: A unique set of allelic Arabidopsis mutants are described that exhibit either suppressed or completely inhibited expression of a gene designated ECERIFERUM9 (CER9). These mutants exhibit a dramatic elevation in the total amount of leaf cutin monomers, and a dramatic shift in the leaf cuticular wax profile toward the very-long-chain free fatty acids (VLCFAs), tetracosanoic acid (C24:0) and hexacosanoic acid (C26:0). Additionally, in cer9 mutants, the cuticle membrane thickness over leaf epidermal long cells is elevated, the cuticular ledges that extend over the stomatal pore are larger, and root suberin is elevated. The cer9 mutation causes delayed wilting in plants experiencing water deficiency, which is due to effects on the shoot and not the root, as revealed by grafting studies. The reduction in whole plant transpiration rate in cer9 is associated with improved water use efficiency, measured as reduced carbon isotope discrimination. Double mutant analysis reveals that cer9 is strongly epistatic to cer8/lacs1 and lacs2, but has overlapping function with cer6 in wax metabolism. By comparison, cer9 is epistatic to cer8/lacs1, but lacs2 is epistatic to cer9, in cutin monomer metabolism. CER9 encodes a predicted E3 ubiquitin ligase, potentially involved in targeting cuticle lipid associated proteins for degradation. Transcriptome analysis revealed a major effect of cer9 on a broad class of metabolic/regulatory networks, with the primary effect on stress-related genes, rather than lipid metabolism genes. Taken together, these results indicate that the CER9 gene product serves as a targeted regulator of cuticle lipid synthesis associated with stress tolerance mechanisms, and as such, may be useful in development of new molecular breeding or transgenic strategies for improving drought tolerance in crop plants.