Sphingolipids are essential components of the outer membrane of plant cells where they contribute to the ability of plants to respond to environmental extremes. Sphingolipids also play important roles in the regulation of basic processes in plant cells, including the initiation of cell death in response to pathogens. Sphingolipids occur in plants as complex mixtures of different chemical structures. The specific contributions of different sphingolipids to the growth and physiology of plants is not well understood. This question will be addressed in this project by the generation of mutants of the model plants Arabidopsis and tomato with defined alterations in sphingolipid structures. These mutants will be characterized by advanced analytical methods to determine the impact on global sphingolipid metabolism. Studies will also be conducted with Arabidopsis and tomato mutants to examine how altered sphingolipid composition affects growth in response to environmental stresses, including drought and high soil salinity. In addition to generating fundamental new knowledge on sphingolipid metabolism and function in plants, the results will provide information that could lead to improving the performance and productivity of crop plants through breeding and biotechnology.
Broader Impacts:
The project will offer educational opportunities and outreach to high school and undergraduate students. The PI and co-PI will participate in the Partnership in Research and Education in Plants, a program that engages high school students in the scientific process by allowing them to devise experiments using mutants of the model plant Arabidopsis. The PI and co-PI will meet with participating students at a Saint Louis, Missouri-area high school and describe the important functions of cellular membranes as well as sphingolipids in human health and plant growth. The students will be provided with seeds for Arabidopsis mutants that they will use for experiments to test hypotheses regarding growth and environmental stress responses. The students will maintain interactions with the PI and co-PI through an online laboratory notebook. The project is also designed to provide research opportunities to undergraduates through the University of Nebraska-Lincoln Undergraduate Creative Activities and Research Experiences (UCARE) program, a two-year program that allows students to conduct literature research and develop an independent research project. Through participation in UCARE, the PI will recruit and mentor an undergraduate student examining the effects of altered sphingolipid composition on growth and physiology of tomato and Arabidopsis.
Membranes of plant cells, which are composed largely of lipids and proteins, play important and diverse roles in the growth of plants and the response of plants to their environment. The lipid components influence the properties of membranes and how membranes function in metabolic and physiological processes. The ability of plants to make specific types of lipids and alter the structures of lipids enables plants to maintain growth and productivity in response to changes in their environment, such as temperature and soil moisture fluctuations. Certain molecules derived from membrane lipids also control basic processes in the plant cell, such as the triggering of cell death. Plants have many different types of lipids that contribute in unique ways to the properties and functions of membranes. This project focused on a class of plant lipids known as sphingolipids that are the most abundant lipids in the plasma membrane or the outer membrane that surrounds the plant cell. We showed that small changes in the structures of sphingolipids in plants can have large effects on the types of sphingolipids that are produced and can strongly impact the physiology of plants. For example, we discovered that plants become extremely sensitive to low temperatures when fatty acid unsaturation is genetically removed from sphingolipids, and that cell death is triggered in these plants by the buildup of molecules known as ceramides. Interestingly, sphingolipid fatty acid unsaturation is absent in many plants, including warm season crops, that are cold sensitive. This information provides a new paradigm for understanding the basic processes of how plants respond to low temperatures and how low temperatures damage plants. Our research also uncovered a role of sphingolipid structure in controlling seed germination rate by altering the permeability of seeds to water. For example, genetic removal of a particular form of unsaturation of sphingolipids in tomato increased seed germination rates by as much as four to seven days. The discoveries made in this project provide basic information about the biochemistry and physiology of plants that will ultimately be useful for engineering or breeding crops with enhanced productivity in response to environmental extremes, such as low temperatures, drought, and soil salinity. The project has also provided a number of educational and outreach opportunities for high school and undergraduate students. These included a research module presented at three Saint Louis, MO high schools designed to teach students about membrane biology through experiments with plant mutants defective in sphingolipid structure. In addition, the project enabled training in laboratory research for five undergraduate students who were active participants in the project. Three of these students have continued their scientific training in graduate programs in biochemistry and plant sciences
