, a Surrogate Host to Study Novel Virulence Mechanisms of Gram-Positive Bacteria, , and in Plants.

is a Gram-positive bacterium that causes bacterial canker and wilting in host plants like tomato. Two major virulence genes encoding a cellulase () and a putative serine protease () have been reported. Here we show that , a commonly used model plant for studying molecular plant-pathogen interactions, is a surrogate host of and . When a low concentration of two species, . and . , were infiltrated into leaves, they caused blister-like lesions closely associated with cell death and the generation of reactive oxygen species and proliferated significantly like a pathogenic bacterium. By contrast, they did not cause any disease symptoms in leaves. The and mutants of . still caused blister-like lesions and cankers like the wild-type strain. When a high concentration of two species and two mutant strains were infiltrated into leaves, all of them caused strong and rapid necrosis. However, only strains, including the and mutants, caused wilting symptoms when it was injected into stems. When two species and two mutants were infiltrated into leaves at the high concentration, they (except for the mutant) caused a strong hypersensitive response. These results indicate that causes blister-like lesions, canker, and wilting in , and and genes are not necessary for the development of these symptoms. Overall, is a surrogate host of species, and their novel virulence factors are responsible for disease development in this plant.