Interplay of pathogens, microRNAs, and regulation of resistance gene transcript abundance for rapid evolutionary responses in plants.

病原体和宿主在世代时间和种群规模上可以有数量级的差异。 这种差异对宿主提出了挑战，以匹配和对抗病原体较短的世代时间（和较大的种群规模）所赋予的快速进化和适应。我们试图调查通过何种方式（即哪些进化遗传变化）植物物种可以匹配其微生物病原体物种的快速进化潜力。 我们工作的重点是宿主-病原体系统，涉及野生番茄物种和卵菌病原体，致病疫霉。 我们将研究microRNA（miR）基因，NBS-LRR抗性基因和病原体抗性在多个野生和驯化番茄物种之间的相互作用。 最近在番茄中发现了一个负调控NBS-LRR基因转录本丰度的miR基因小家族。 这些miR基因的上调导致NBS-LRR抗性基因的下调，反之亦然。 因此，miRNA丰度可能与植物的抗病水平有关。 R基因的转录后控制可以允许植物对病原体攻击进行更快速的防御反应，因此可能是植物中部署的适应以匹配其病原体的进化潜力。 然而，R基因的转录后控制也可以被病原体劫持以抑制防御反应。 我们预测植物中病原体的存在确实会影响miR转录本的丰度，并随后影响R蛋白的丰度。 在一个极端，病原体上调miR基因或分泌miR分子模拟物将下调R基因丰度。 这将被视为病原体的一种适应。 或者，病原体下调这些miR基因将导致R基因上调。 在这种情况下，抗性将被激活，植物将占据优势。 这两种情况都让我们深入了解了这些物种之间发生的复杂的相互进化遗传变化。 在这项研究计划中，我们想通过一个小的miR基因家族的成员在病原体感染的存在下，研究R基因的转录后调控。 我们将使用四种不同的病原体基因型对八种不同的番茄品种进行控制接种。 将确定病原体传播和宿主抗性的水平。 同时，我们将检测感染过程中7个miR基因的初级和成熟转录本的丰度。 我们还将分析这些miR转录物靶向的8个推定的致病疫霉抗性基因的转录物丰度。 通过多变量统计分析，我们将能够确定哪些miR基因和哪些R基因在病原体感染过程中上调或下调。 这些基因将进行进一步的功能研究，在植物，验证。

Pathogens and hosts can differ by orders of magnitude in their generation time and population sizes. This difference presents a challenge for hosts to match and counter the rapid evolution and adaptation endowed by the shorter generation times (and larger population sizes) of pathogens. We seek to investigate by which means (i.e. which evolutionary genetic changes) plant species can match the rapid evolutionary potential of their microbial pathogen species. The focus of our work is the host-pathogen system involving wild tomato species and the oomycete pathogen, Phytophthora infestans. We will investigate the interplay of microRNA (miR) genes, NBS-LRR resistance genes, and pathogen resistance across multiple wild and domesticated tomato species. A small family of miR genes that negatively regulates transcript abundance of NBS-LRR genes has recently been discovered in tomato. The up-regulation of these miR genes leads to the downregulation of NBS-LRRs resistance genes, and vice-versa. Therefore, miRNA abundance is likely tied to levels of disease resistance in plants. Post-transcriptional control of R-genes may allow the plants to mount a more rapid defense response to pathogen attack and thus may be an adaptation deployed in plants to match the evolutionary potential of their pathogens. However, post-transcriptional control of R-genes can also be hijacked by pathogens to suppress defense responses. We predict that presence of pathogens in plants does affect the miR transcript abundance and subsequently the R-protein abundance. At the one extreme, pathogen up regulation of miR genes or secretion of miR molecular mimics would down regulate R-gene abundance. This would be viewed as an adaptation on the part of the pathogen. Alternatively, down-regulation by the pathogen of these miR genes would lead to up-regulation of R-genes. In this case, resistance would be activated and the plant would have the advantage. Either scenarios give us insight into the complex reciprocal evolutionary genetic changes that have taken place between these species. In this research initiative, we would like to investigate the post-transcriptional regulation of R-genes through members of a small miR gene family in the presence of pathogen infection. We will conduct controlled inoculations of eight different tomato species using four different pathogen genotypes. The level of pathogen spread and host resistance will be determined. Simultaneously we will assay the abundance of the primary and mature transcripts of seven miR genes during the infection. We will also assay the transcript abundance of eight putative P. infestans resistance genes, targeted by these miR transcripts. Through multivariate statistical analyses, we will be able to identify the which miR genes and which R-genes are up- or down-regulated during pathogen infection. These genes will be subjected to further investigation for functional, in planta, validation.