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

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

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.