Arabidopsis plants inoculated with Erysiphe pisi fungal spores are shown here. From left to right, plants with no mutations (WT), a disabled PEN2 gene, disabled PAD4 and SAG101 genes, and all three disabled genes together are increasingly vulnerable to the fungus. This last variant is the most susceptible to infection; it allowed E pisi to proliferate as well as it does on pea plants, its normal host. (Images printed with permission from the American Association for the Advancement of Science, Science, November 18, 2005, issue.) News Release