A plant MAPK cascade in effector-triggered immunity: role of chloroplast-originated reactive oxygen species

光合作用对作物产量和产量至关重要。植物在病原体攻击下表现出光合作用能力降低，但导致这种下降的分子机制尚不清楚。目前还不清楚这种减少是一个主动调节的过程，还是病原体侵染和植物活力恶化的被动结果。在研究这两个关键信号蛋白在植物免疫中的作用的过程中，人们发现，在病原菌侵袭过程中，这些蛋白的激活迅速而主动地下调植物光合作用装置的各种成分和活性，导致光下叶绿体产生活性氧。这些事件对植物抵抗病原菌很重要，但同时也损害了光合作用的活性。在这个项目中，研究人员将确定这一途径中的未知成分。基因组、分子遗传学、生化和生理学方法的结合将为学生和博士后提供良好的培训环境。来自代表性不足群体的学生(包括研究生和本科生)和博士后将通过参加面向少数族裔的机构项目积极招募。光合作用是作物生产的关键，植物防御总是与光合作用活性降低有关，这反过来又会对植物的生长和产量产生负面影响。因此，在我们通过平衡这两个关键功能来培育增强免疫力和生长/产量的作物之前，我们必须了解调节这两个关键功能相互作用的机制。丝裂原活化蛋白激酶(MAPKs)MPK3/MPK6参与植物病原菌应答的MAPK信号转导通路，在病原相关分子模式(PAMP)触发的免疫(PTI)和效应器触发的免疫(ETI)中发挥重要作用。在ETI过程中，MPK3/MPK6的长期激活导致植物光合作用的主动下调，其机制包括mRNA失稳。植物的防御不仅涉及基因表达的上调，这一点已经引起了相当大的关注，而且还涉及到下调。看家基因转录的快速下调，例如那些与植物光合作用有关的基因，经常需要mRNA的不稳定。已经确定了信使核糖核酸降解机制的组成部分，然而，调控途径(S)在很大程度上是未知的。在这个项目中，研究人员将使用一种综合的方法来识别和功能分析这一途径中的未知成分。破译植物免疫过程中MPK3/MPK6级联调控基因稳定性的机制(S)，是我们理解植物基因表达调控的基础。MPK3/MPK6在调控植物光合作用、叶绿体中的活性氧产生、超敏反应介导的细胞死亡以及植物免疫等方面的进一步研究将是该领域在分子水平上的重大进展。这项研究也将阐明MPK3/MPK6级联在核-叶绿体通讯和逆行信号转导中的作用。对光合作用和免疫之间的相互作用有更深入的了解，这两个过程对作物生产力有重大影响，应该有助于作物改良的努力，以支持生产足够的食物/饲料/生物燃料来维持日益增长的世界人口。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Photosynthesis is essential to crop productivity and yield. Plants under pathogen attack plants show reduced photosynthetic capacity but the molecular mechanism responsible for this downturn is unknown. It is also unclear whether the reduction is an actively regulated process or a passive result of pathogen infestation and deterioration of plant vigor. In the process of studying the function of two key signaling proteins in plant immunity, it was discovered that the activation of these proteins during pathogen attack rapidly and actively down-regulates various components and activities of the plant photosynthetic apparatus, leading to the generation of reactive oxygen in chloroplasts under light. These events are important to plant resistance against pathogens but at the same time compromise photosynthetic activity. In this project, the investigators will identify unknown components in this pathway. The combination of genomic, molecular genetic, biochemical, and physiological approaches to be used 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 by participating in institutional programs that reach out to minorities. Photosynthesis is key to crop production, and plant defense is always associated with reduced photosynthetic activities, which, in turn, negatively impacts plant growth and yield. Therefore, it is important that we understand the mechanisms that mediate the interaction of these two key functions before we can breed both enhanced immunity and growth/yield in crops by balancing the two sides. The mitogen activated protein kinases (MAPKs) MPK3/MPK6 participate in plant pathogen-responsive MAPK signaling cascade that plays important roles in both pathogen associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI). Long-lasting activation of MPK3/MPK6 during ETI results in active down-regulation of plant photosynthesis via a mechanism which includes mRNA destabilization. Plant defense involves not only up-regulation of gene expression, which has received considerable attention, but also down-regulation. Rapid down-regulation of transcripts of housekeeping genes such as those involved in plant photosynthesis frequently requires mRNA destabilization. Components of the mRNA degradation machinery have been identified, however, the regulatory pathway(s) are largely unknown. In this project the investigators will use an integrative approach to identify and functionally analyze the unknown components in this pathway. Deciphering the mechanism(s) underlying the regulation of mRNA stability by the MPK3/MPK6 cascade during plant immunity is fundamental to our understanding of plant gene expression regulation. Further characterization of MPK3/MPK6 in regulating plant photosynthesis, reactive oxygen species generation in chloroplasts, hypersensitive response mediated cell death, and plant immunity at molecular level will be a major advance in the field. This research will also shed light on the function of MPK3/MPK6 cascade in nucleus-chloroplast communication and retrograde signaling. A deeper understanding of the interplay between photosynthesis and immunity, two processes that have major impacts on crop productivity, should facilitate efforts at crop improvement in support of the production of sufficient food/feed/biofuel to sustain the increasing world population.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.