Molecular Mechanism of MAPK Phosphorylation-Induced Stabilization of ACC Synthase and Ethylene Production in Plants under Stress

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Mitogen-activated protein kinase (MAPK) cascades are conserved eukaryotic signaling modules that transduce extracellular stimuli into intracellular responses. Plant MAPKs are implicated in regulating plant growth, development, and responses to environmental stress. However, the underlying mechanisms in plants by which signals are perceived and transduced are unknown. The long-term goal of this project is to elucidate the functions and mechanisms of actions of two plant stress-responsive MAPKs. Recently, the PI found that in response to stress these MAPKs modulate the biosynthesis of ethylene, a plant stress hormone, by influencing the stability of an ethylene biosynthetic enzyme that responds to stress (ACS2/ACS6). The focus of this project is to investigate how the phosphorylation ACS2/ACS6 leads to its stabilization. Three potential mechanisms will be evaluated: i) phosphorylation triggers the binding of a protein that prevents the degradation of phosphorylated ACS2/ACS6; ii) phosphorylation prevents the binding of a protein that targets unphosphorylated ACS2/ACS6 to degradation; and iii) the combination of the above two. This project will impact three major areas of plant research, including i) the molecular mechanism of plant MAPK function, ii) the regulation of plant hormone biosynthesis, and iii) the regulation of ubiquitin-proteasome mediated protein degradation by phosphorylation and dephosphorylation. A combination of biochemical, proteomic, molecular, and genetic approaches will be used, which will provide an excellent training environment for students and post-docs. Training of students and post-docs who can take an integrative approach to study a biological phenomenon is critical to the advance of post-genome biology. In addition, undergraduate students, especially those from under-represented groups, will be actively recruited through institutional programs that reach out to minorities. Ethylene plays important roles in the adaptation of plants to adverse environmental conditions, in addition to its role in regulating growth and development. One potential application of this work is that the identification of important regulatory components in MAPK-mediated ethylene induction pathway may lead to the generation of crops with enhanced stress tolerance, therefore, allowing the use of marginal land for crop production.