Arabidopsis: A weed leading the field of plant-pathogen interactions

Arabidopsis thaliana, like other flowering plants, exhibits specificity in resistance to plant pathogens. Using the genetic diversity present in differential accessions of Arabidopsis, over 49 loci which govern pathogen specificity have been identified. Similar to resistance genes from other plant species, the Arabidopis RPS2, RPM1, and RPP5 resistance genes encode leucine-rich repeat proteins, suggesting that Arabidopsis behaves in a manner similar to other angiosperms in disease resistance mechanisms. Novel insights into events subsequent to pathogen recognition in Arabidopsis have been obtained from analysis of mutants altered in defense. Not only have signal transduction pathways been deduced, but several genes involved in post-recognition events have been cloned using positional cloning methods. One such gene, NPR1, encodes an ankyrin-repeat protein with similarity to animal proteins which regulate the inflammatory response in mammalian cells and antifungal responses in Drosophila, suggesting an ancestral link in defense responses between the animal and plant kingdoms. NPR1 is not alone in providing novel insights into the mechanism(s) of disease resistance, the ein2 and hls1 mutants have clearly demonstrated that ethylene has a role in plant defense, and the cloning of the LSD1 gene provides a molecular tool to examine reactive oxygen species in programmed cell death.