Genetic analysis of induced systemic resistance in Arabidopsis thaliana: association between induced and basal resistance

Abstract

Selected nonpathogenic rhizobacteria are able to elicit induced systemic resistance (ISR) in plants. Different ecotypes of Arabidopsis thaliana were screened for expression of ISR against infection by Pseudomonas syringae pv. tomato, after treatment of the roots with the nonpathogenic P. fluorescens strain WCS417r. From the seven ecotypes tested, two ecotypes (RLD and Ws-0) did not develop ISR after treatment with P. fluorescens strain WCS417r. This ISR-nonresponsive phenotype was correlated with a remarkably low level of basal resistance, suggesting that the ability to express ISR is dependent on a threshold level of basal resistance. Subsequently, a cross was made between an ISRresponsive (Col-0) and an ISR-nonresponsive ecotype (RLD). F₁ hybrids were fully capable of expressing ISR and exhibited a relatively high level of basal resistance, indicating that the potential to express ISR and basal resistance are both inherited as dominant traits. Analysis of F₂ plants revealed that both traits segregated in a 3: 1 fashion in the same set of plants, indicating that the potential to express ISR and basal resistance are monogenically determined and presumably linked.