Starter Grant: The Effect of Molecular Variation in Disease Resistance Genes in Phenotypic Expression of Resistance in Plants

该项目的目标是弥合抗病基因的分子遗传学和抗病自然变异遗传结构的QTL研究之间的差距。研究者将使用候选基因分析来测试拟南芥抗性基因的分子变异与对丁香假单胞菌的抗性的定量表型变异之间的关系。拟南芥与丁香拟南芥的互作是研究这种关联的理想系统。拟南芥（a.thaliana）是研究植物抗病分子基础的一个模式系统，已经鉴定出4个抗病基因（R基因），在丁香假单胞菌侵染植物时识别并触发防御反应。其中两个基因，RPS4和RPS5，与研究者在博士后研究中发现的QTL非常接近；QTL影响丁香假单胞菌抗性的数量变异。这提出了这些R基因也定量影响植物对病原体攻击的反应的可能性。这两个QTL的效应非常大，显性效应显著，与R基因的预期一致。为了确定RPS4和RPS5基因的分子变异是否有助于在拟南芥中观察到的数量变异，将对来自世界各地的拟南芥收集的19个材料进行这两个基因的测序，这些材料之前被证明在对丁香假单胞菌的抗病性方面存在数量差异。这些品种的分子和表型变异之间的关联将使用方差的嵌套分析进行检验。重要的结果将表明，在这些基因的进化史中，一个给定的突变导致了与平均抗病表型的显著偏差。这些信息将大大增加我们对这些基因进化的理解，并为这些基因的功能作用提供见解。了解分子变异如何影响定量表型变异是进化生物学以及农业和医学遗传学的一个重要目标。尽管最近人们对数量性状的遗传结构和关键基因的分子进化有了很多了解，但很少有研究试图将这两个领域联系起来。这项研究将是弥合这两个领域之间差距的重要一步，并进一步加深我们对植物抗病的分子基础的理解。

The goal of this project is to bridge the gap between the molecular genetics of disease resistance genes and QTL studies examining the genetic architecture of natural variation in disease resistance. The investigator will use a candidate-gene analysis to test for associations between molecular variation in well-characterized resistance genes of the plant Arabidopsis thaliana and quantitative phenotypic variation in disease resistance to the bacteria Pseudomonas syringae. The interaction between A. thaliana and P. syringae is an ideal system in which to investigate such association. A. thaliana has been a model system for studies of the molecular basis of disease resistance in plants, and four resistance genes (R genes) have been identified that recognize and trigger defense responses in plants challenged with P. syringae strains. Two of these genes, RPS4 and RPS5, are located very close to QTL the investigator identified during her postdoctoral research; the QTL affect quantitative variation in resistance to P. syringae. This raises the possibility that these R genes also affect the plant's response to pathogen attack quantitatively. These two QTL had very large effect and a significant dominance effect, as is expected for R genes. To determine whether molecular variation in the RPS4 and RPS5 genes contribute to the quantitative variation observed among A. thaliana accessions, the two genes will be sequenced in 19 accessions from a world-wide collection of A. thaliana previously shown to vary quantitatively in disease resistance to P. syringae. Associations between molecular and phenotypic variation among these accessions will be tested using a nested analysis of variance. Significant results will indicate that a given mutation during these genes' evolutionary history has caused a significant deviation from the average disease resistance phenotype. Such information will significantly increase our understanding of the evolution of these genes and provide insights into the functional role of these genes. Understanding how molecular variation affects quantitative phenotypic variation is an important goal of evolutionary biology as well as of agricultural and medical genetics. Although much has been learned recently about the genetic architecture of quantitative traits and about the molecular evolution of key genes, very few studies have attempted to link the two fields. This research will be an important step toward bridging the gap between these two fields and in furthering our understanding of the molecular basis of disease resistance in plants.