Use of transient expression in plants for the study of the “gene-for-gene” interaction

Abstract

One of the common responses in disease resistance defined by the "gene-for-gene" interaction is the hypersensitive response (HR), which is a rapid and localized cell death of plants at the site of infection. This specific cell death was used to develop a biolistic transient expression assay for the resistance response. If the transiently expressed gene causes the HR, the expression level of a cointroduced reporter gene decreases due to the rapid death of the cell. Using this assay, it was shown that expression of the Pseudomonas syringae avirulence genes, avrRpt2 or avrB, in Arabidopsis thaliana can elicit the HR when the plants carry the corresponding resistance gene, RPS2 or RPM1, respectively. This indicates that the avirulence genes are the only bacterial factors that are required to elicit the specific resistance response as long as the avirulence gene products are localized properly. This observation and others strongly suggest that the molecular recognition of pathogen attack occurs inside of plant cells for these combinations of avirulence gene and resistance gene. RPS2 and RPM1 are members of NBS-LRR class of resistance genes. NBS-LRR proteins could be cytoplasmic receptors for specific signal molecules from avirulent pathogens. We propose a speculative model to view different classes of resistance gene products from a unified perspective.