the type III secretion system discovered in the early nineties, is an essential part of the arsenal of plant pathogenic bacteria. This molecular syringe can directly inject bacterial proteins (called type III effectors of T3E) into the host plant cell.
It has been shown that this mechanism is an essential part in the control of virulence and aggressiveness of different bacterial strains on different host plants. Plant resistance proteins can detect the presence of these T3E and provide strong isolate-specific resistance to the host plants.
Here you can find a selection of papers related to the study of T3E from plant pathogenic bacteria