Ruth Welti and Gary L. Gadbury, Kansas State University Jyoti Shah, University of North Texas Xuemin (Sam) Wang, University of Missouri, St. Louis and Danforth Plant Science Center
Increasing evidence indicates that environmental stresses, such as freezing, high salinity, and pathogen infection, lead to oxidative modification of plant membrane lipids to produce "ox-lipids". In contrast to oxylipins, such as jasmonic acid and its derivatives, whose significance in plant growth and defense against stress has been well documented, little is known about the functions of ox-lipids in plants. Ox-lipids may function as mediators signaling stress responses, they may represent damage that could serve as a protective buffer against oxidative damage elsewhere in the cell, or they may be long-term modifications that might function as stress "memory". Thus, ox-lipids have the potential to be essential mediators of plant response to the environment. The goals of the research project are to understand the role of ox-lipids in plant responses to biotic and abiotic stresses and to determine the function of members of two enzyme families, lipoxygenases and acyl hydrolases, which are likely to play important roles in the metabolism of oxidized lipids. The project will test the hypotheses that patterns of ox-lipids are fingerprints of individual stresses and that production and/or removal of specific ox-lipids by lipoxygenases and acyl hydrolases contributes to plant adaptation to stress. Under freezing and high salinity stress (abiotic stress) and infection by a fungal pathogen, Botrytis cinerea, and a bacterial pathogen, Pseudomonas syringae (biotic stresses), the stress-response phenotype and production of ox-lipids by wild-type plants and lipoxygenase- and acyl hydrolase-deficient mutant plants will be documented. The data will shed light on the roles of lipoxygenases and acyl hydrolases in stress responses and in production of specific ox-lipid patterns. Analysis of the stress-phenotype and ox-lipid profiles will lead to identification of ox-lipids that are candidates for mediating plant stress responses. The function of candidate lipid mediators will be tested by lipid analysis and phenotypic analysis of plants overexpressing enzymes that produce the candidate lipids and by supplementing mutant and wild-type plants with the putative mediators. The results have the potential to fill critical gaps in understanding of how lipid metabolic enzymes, cellular lipids, and their metabolites interact to influence plant performance.
Broader Impacts: Carrying out the proposed work will provide training for multiple students and postdoctoral trainees at four institutions and bring current knowledge of metabolic profiling, functional genomics, and stress biology to the classroom. It will broaden the participation of underrepresented groups in research through the McNair Program at the University of North Texas, the Summer Undergraduate Research Opportunity Program at Kansas State University, the Des Lee Collaborative Scholarships at the University of Missouri, and the Danforth Plant Science Center NSF REU-Site program, which has achieved over 30% participation by underrepresented minority groups in the past several years. It will involve high school students in the research through the Texas Academy of Mathematics and Science at University of North Texas and through the Students and Teachers as Research Scientists (STARS) program in St. Louis. Organization of mass spectral data on plant lipids, and particularly on stress-induced lipids, into a web-accessible database will provide a foundation for further investigation of the structure and function of lipids, and particularly novel lipids, and will facilitate integration of lipidomics data with other metabolomics and functional genomics data. Analytical capabilities developed in this work will become enabling technologies available to researchers worldwide via the Kansas Lipidomics Research Center. This work also will provide insight into the identity of metabolic steps with potential to enhance stress tolerance in plants and improve agricultural productivity and quality.
The research goals of the collaborative project (MCB 0920663, 0920600, and 0920681) were to understand the role of lipids in plant responses to biotic and abiotic stresses. Stresses, including pathogen infections, drought, temperature changes, and nutrient deficiencies, pose serious challenges for agricultural productivity. In particular, we investigated the function of two classes of enzymes, lipoxygenases (LOXs) and acyl hydrolases (AHs), in the metabolism of lipids, and particularly oxidized lipids, in plant stress responses. To carry out the project, we compared levels of many lipids from a plant with a mutation knocking out the function of a particular enzyme with levels of lipids in a wild-type plant. This is a straightforward, powerful, and unbiased approach to identifying the function of a knocked-out enzyme that acts in lipid metabolism. To measure many different types of lipids in a single sample, analytical methods were expanded. The ability to analyze lipids by mass spectrometry was greatly increased. Many previously undescribed lipids were documented. The lipid compositional changes that occur when plants are subjected to bacterial infection, fungal infection, day-night cycles, water stress, mechanical wounding, nitrogen deficiency, and phosphate deficiency were determined. Roles of particular lipid-metabolizing enzymes in these processes and in plant development and seed oil production were identified. Information gained from these studies is now being applied to enhance oil production in plants and develop wheat plants with enhanced disease resistance. The lipid analytical technology has been made available to other scientists, who have employed it to investigate a wide range of research problems, ranging from plant-related work to biomedical. An online tool to do necessary calculations on mass spectrometry data to produce lipid compositional data was also developed and made available to the scientific community. The collaborative group broadly trained students in plant biology, biochemistry, and data analysis, and mentored students to prepare them for careers in science and related fields. This project has provided continued education for five faculty members, two technical professionals, five postdoctoral trainees, three graduate students, twenty-four undergraduate students, and four high school students. The students worked and learned at Kansas State University, University of Missouri-St. Louis, University of North Texas, and/or Langston University.
