Mitogen-activated protein kinase (MAPK, or MPK) cascades are conserved signaling modules that play vital roles in all eukaryotic organisms. Arabidopsis MPK3 and MPK6, as well as their functional equivalents in other species, are implicated in plant disease resistance. However, the underlying mechanism is unclear. Recently, it was discovered that activation of MPK3 and MPK6 induces cyanide accumulation, which leads to the generation of reactive oxygen species (ROS) in chloroplasts and cell death during the hypersensitive response. In this project, the investigators will use a combination of physiological, biochemical, and molecular genetic approaches to understand the regulation of cyanide accumulation during plant defense response and to generate plants with either elevated or reduced cyanide accumulation. Phenotypic analyses of these plants will provide in vivo gain- and loss-of-functional evidence to establish cyanide as a new regulatory/signaling molecule in plants. Cyanide is a co-product of ethylene biosynthesis. As a plant hormone, ethylene has been the focus of much study, its role in plant physiological and developmental processes, as well as the mechanisms of ethylene action have been investigated extensively. However, cyanide as a regulatory molecule in plants has been mostly ignored, despite its obvious biological effects on a number of critical enzymes and processes in cells. Broader impacts. The use of a combinatory approach in this project will provide an excellent training environment for students and post-docs. Students (both graduate and undergraduate) and post-docs from under-represented groups will be actively recruited though participation in institutional programs which reach out to such scientists. Cyanide is a potent inhibitor of various activities in chloroplasts and mitochondria, two organelles known as cellular 'power plants'. Understanding the regulation of cyanide accumulation and its functions in energy conversion, ROS generation, and HR cell death may lead to the generation of crops with enhanced yield under stress conditions. This is important for agriculture to produce enough food/feed and harvestable energy to meet an increasing demand.
Pathogens and abiotic stresses cause major loss in our crop production each year. Understanding of how plants defend themselves against invading pathogens and how they adapt to stress conditions is key to the development of new strategies to increase food/feed production on limited arable land. Plant defense/stress responses are regulated by a complex network of signaling events after plant sensing of pathogens or stresses. Among these signaling events, activation of mitogen-activated protein kinases (MAPKs) is one of the earliest responses. MPK3 and MPK6, two Arabidopsis pathogen/stress responsive MAPKs, as well as their functional equivalents in other plant/crop species, are implicated in disease resistance and adaptation to abiotic stresses. However, the underlying mechanism is unclear. Recently, we discovered that the activation of MPK3 and MPK6 induces the biosynthesis of ethylene, an important plant stress hormone. ACC synthase (ACS) is the rate-limiting enzyme in ethylene biosynthetic pathway. MPK3 and MPK6 regulate ethylene synthesis by directly phosphorylating two ACS isoforms (ACS2 and ACS6), which stabilizes the ACS protein and enhances ethylene production. Long-lasting activation of MPK3 andMPK6 also leads to the generation of reactive oxygen species (ROS) in chloroplasts and hypersensitive response (HR) cell death, two events associated with pathogen resistance. In plants, cyanide is a co-product of ethylene biosynthesis and is produced at 1:1 molar ratio with ethylene. We found that the activation of MPK3/MPK6 also results in cyanide accumulation, which proceeds the generation of ROS and HR-like cell death. In this project, we used a combination of genetic, biochemical, and physiological approaches to investigate the role of MPK3/MPK6-regulated cyanide production in signaling plant defense responses. As a plant hormone, ethylene received a lot of attention and its roles and mechanisms of actions have been investigated extensively. However, our understanding of cyanide is very limited, despite its obvious biological effects on a number of critical enzymes/processes in cells. The results from this project have been published in two scientific journal articles, and additional manuscripts are in preparation. The use of a combinatory approach in this project provided an excellent training environment for students and post-docs. Several students, including one high school student, three undergraduate students, and one graduate student, and one post-doc were involved in this project. Participation of high-school students in this research project sparked their interest in life sciences and benefited the training of future generation of scientists. This project also allowed the training of a summer intern from a liberal art college as part of the MU Life Sciences Undergraduate Research Opportunity Program (LSUROP, www.lsurop.missouri.edu/). Hands-on research is an excellent way for students to learn the scientific method, and to collaborate with their peers. Engaging students by allowing them develop and carry out research projects not only helps them understand biological processes, but also develops their critical thinking skills. Cyanide is a potent inhibitor of various activities in chloroplasts and mitochondria, two organelles known as cellular 'power plants'. Understanding the regulation of cyanide accumulation and its functions in energy conversion, ROS generation, and HR cell death may lead to the generation of crops with enhanced yield under stress conditions. This is important for agriculture to produce enough food/feed and harvestable energy to meet the increasing demand.
