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

丝裂原活化蛋白激酶(MAPK)级联是真核生物中保守的信号模块，将细胞外刺激转化为细胞内反应。植物MAPK参与调节植物的生长、发育和对环境胁迫的反应。然而，植物中感知和传递信号的潜在机制尚不清楚。本项目的长期目标是阐明两个植物逆境反应MAPK的功能和作用机制。最近，PI发现，在对胁迫的响应中，这些MAPK通过影响响应胁迫的乙烯生物合成酶(ACS2/ACS6)的稳定性来调节乙烯的生物合成。本项目的重点是研究ACS2/ACS6的磷酸化如何导致其稳定。将评估三种可能的机制：i)磷酸化触发蛋白质的结合，防止磷酸化的ACS2/ACS6降解；ii)磷酸化防止针对未磷酸化的ACS2/ACS6的蛋白质结合降解；以及iii)以上两者的组合。该项目将对植物研究的三个主要领域产生影响，包括：(1)植物MAPK功能的分子机制；(2)植物激素生物合成的调控；(3)泛素-蛋白酶体通过磷酸化和去磷酸化调节蛋白质降解。将结合生物化学、蛋白质组学、分子和遗传学方法，为学生和博士后提供良好的培训环境。培养能够采取综合方法研究生物现象的学生和博士后，是推进后基因组生物学的关键。此外，将通过面向少数族裔的机构项目积极招收本科生，特别是来自代表性不足群体的本科生。乙烯除了调节植物的生长发育外，还在植物适应恶劣环境条件方面发挥着重要作用。这项工作的一个潜在应用是，识别MAPK介导的乙烯诱导途径中的重要调控成分可能导致产生抗逆性增强的作物，从而允许利用边际土地进行作物生产。

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.