Characterization of Systemin-responsive MAP Kinase Cascades

虫害给美国和世界各地的农民造成了巨大的损失。开发对草食性昆虫具有更高抗性的改良植物对于提高产量、降低生产成本和使用对环境有害的杀虫剂非常重要。了解植物对昆虫的防御反应的关键是导致防御基因上调的潜在信号通路。在番茄、马铃薯和其他茄科植物中，对咀嚼昆虫的反应是由一种类似激素的短信号肽系统素介导的。系统素是成功防御昆虫所必需的，其信号转导途径是明确的。一个主要的进展是最近发现了系统蛋白受体SR160，它是一种LRR受体激酶。令人惊讶的是，SR160与番茄油菜素类固醇(BR)受体tBRI1相同。BRs在植物发育中起着重要的作用。因此，番茄为研究受体SR160/tBRI1与系统蛋白和BRs的相互作用如何导致胁迫或发育反应提供了一个独特的机会。这种双配体受体以前从未在植物中被发现，可能是一种全新的信号传递方式。MAPK是逆境信号传递到防御基因的中心。它们是MAPK级联的一部分，MAPK级联由三个功能相连的激酶组成。MAPK级联通常以受体依赖的方式被激活，但连接受体和MAPK级联的组件尚不清楚。这项研究的重点是确定连接SR160/tBRI1受体和系统反应MAPK的组件和机制。作为第一步，系统反应MAPK激酶(MAPKK)将通过酵母双杂交系统进行鉴定。MAPKK直接作用于MAPK的上游。利用突变植株和番茄原生质体瞬时转化系统，将在体内测试这些MAPKK是否激活MAPKs以响应系统素，以及这是否需要SR160/tBRI1。如果这些MAPKK的结构性活性突变体的表达导致转基因植物中防御基因的上调和对草食性昆虫的抗性增强，也将进行测试。操纵MAPK级联已被认为是培育抗逆性作物的一种非常有前途的工具。推测系统素和BRS的信号转导在SR160/tBRI1受体下游发散，BRS不激活MAPKs。如果BRS确实激活了MAPK，这些MAPK将被进一步表征。阐明通过双配体受体的独特信号模式将导致对信号感知和转导的新见解，这可能比先前假设的更常见。综上所述，这个项目将增加对信号机制如何调控植物逆境反应的理解。该项目将涉及一名博士后研究助理、一名研究生和本科生，他们将接受最先进的植物分子生物学方法培训。本科生有机会获得实践研究经验，这对他们的职业发展至关重要。与该项目相关的研究将纳入本科生和研究生的高级班级，由PI授课。将积极招募任职人数不足的团体参加该项目。

Insect pests cause huge losses to farmers in the U.S. and worldwide. Developing improved plants with increased resistance to herbivorous insects is important for increasing yields while reducing production costs and the use of environmentally harmful insecticides. A key for understanding plant defense responses to insects are the underlying signaling pathways that result in upregulation of defense genes. In tomato, potato and other solanaceous plants, the response to chewing insects is mediated by a hormone-like short signaling peptide, systemin. Systemin is essential for successful defense against insects, and its signaling pathway is well defined. A major advance was the recent identification of the systemin receptor SR160, a LRR-receptor kinase. Surprisingly, it was shown that SR160 is identical to tBRI1, the tomato brassinosteroid (BR) receptor. BRs play an important role in plant development. Thus, tomato provides a unique opportunity to study how interactions of the receptor SR160/tBRI1 with systemin and BRs result in either stress or developmental responses. Such dual ligand receptors had not been identified in plants before and may be an entirely new way of signaling.MAPKs are central for the relay of stress signals to defense genes. They are part of the MAPK cascade, which consists of three functionally linked kinases. The MAPK cascade is often activated in a receptor-dependent manner, but the components that link receptors and MAPK cascades are not known. The focus of the proposed research is to identify the components and mechanisms that connect the receptor SR160/tBRI1 to the systemin-responsive MAPKs. As a first step, systemin-responsive MAPK kinases (MAPKKs) will be identified by employing the yeast two-hybrid system. MAPKKs function directly upstream of MAPKs. Using mutant plants and a tomato protoplast transient transformation system, it will be tested in vivo if these MAPKKs activate MAPKs in response to systemin, and if this requires SR160/tBRI1. It will also be tested, if expression of constitutively active mutants of these MAPKKs results in upregulation of defense genes and increased resistance against herbivorous insects in transgenic plants. Manipulation of MAPK cascades has been realized to be a very promising tool to generate stress resistant crop plants. It is hypothesized that signal transduction for systemin and BRs diverges downstream of the receptor SR160/tBRI1, and that BRs do not activate MAPKs. If BRs do activate MAPKs, these MAPKs will be further characterized. Elucidating the unique mode of signaling via a dual ligand receptor will lead to new insights in signal perception and transduction that is likely to be more common than previously assumed. Taken together, this project will increase the understanding of how signaling mechanisms regulate plant stress responses.The project will involve a postdoctoral research associate, a graduate student and undergraduate students who will be trained in state-of-the-art methods in plant molecular biology. Access to hands-on research experience for undergraduate students is crucial for the development of their careers. Research related to this project will be incorporated in an upper level class for undergraduate and graduate students, taught by the PI. Underrepresented groups will be actively recruited to participate in the project.