Submitted to: Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2011
Publication Date: January 31, 2012
Citation: Halgren, A.B., Banowetz, G.M. 2012. Life cycle expression analysis of three cell wall degradation-related genes in ethylene-treated grass. Plant Growth Regulation. 66: 167-177. Interpretive Summary: Ethylene is a plant hormone that regulates fruit ripening, flower formation, and a number of other processes during plant development. Not much is known regarding the role of this hormone in responding to stress, or in wounding like that which occurs when forage grasses are harvested. We had interest in learning whether ethylene plays a role in harvest-associated wounding because of the potential to use forage grasses as potential feedstock for bioenergy production. If we understand the response of these grasses to wounding, we can improve their re-growth characteristics and their potential utility as bioenergy substrates. We studied the role of ethylene in affecting the types of genes that were expressed during different growth stages and found that ethylene apparently affects different genes as forage grasses mature. We particularly focused on the impact of ethylene on the regulation of cell-wall degradation genes because these will have practical utility in future development of approaches for cellulosic ethanol production.
Technical Abstract: Ethylene regulates multiple developmental processes during a plant life cycle, but the effect of ethylene on the upregulation of senescence-, stress-, and post-harvest-related genes in forage grasses is poorly understood. In this work, we used quantitative PCR to determine whether ethylene application affected the expression of selected cell-wall degradation related genes that are typically upregulated post-harvest. The expression levels of beta-D-glucan exohydrolase isoenzyme, alpha glucosidase, and arabinoxylan arabinofuranohydrolase isoenzyme, all putative cell wall degrading enzymes, were quantified at six points in the life cycle of the model grass species Darnel ryegrass (Lolium temulentum L.). We also quantified the expression of ACC oxidase and ACC synthase in response to ethylene application to determine if endogenous upregulation of ethylene biosynthesis occurred. Grass developmental stage had a significant impact on gene expression response to ethylene-treatment, indicating that discrete life cycle stages present different ethylene-responsive windows for treatment. Under our experimental conditions, ACC oxidase and ACC synthase expression were downregulated in response to ethylene-treatment, suggesting that exogenous ethylene served an auto-inhibitory role. Transcripts corresponding to the three cell wall degradation related genes increased significantly in response to ethylene treatment, suggesting that ethylene may have future utility in the pretreatment of lignocellulosic biomass. To our knowledge, this is the first report of a life cycle analysis of ethylene-induced genes in forage grasses.