Effectors from the YopJ/HopZ/AvrBsT group: suppression of effector-triggered immunity and contribution to virulence in tomato and other plants of agronomic relevance

摘要

Bacterial pathogens face a two-tiered plant defense response, which starts with basal resistance as a consequence of the recognition of bacterial conserved molecular patterns, such as flagellin. Many bacterial pathogens use a type-Ill secretion system(T3SS) to deliver effector proteins (T3Es) inside the plant cell cytosol, thus suppressing basal defense. However, detection of such effectors by the plant immune system can trigger an additional response, resulting in resistance against the pathogen. This second line of defense can in turn be suppressed by the activity of additional effectors, included in the effector repertoire of the pathogen. Pseudomonas syringae and Xanthomonas campestris strains, causal agents of a wide variety of diseases to economically important crops, are among the best-characterized bacterial pathogens that utilize a T3SS to translocate complex effector repertoires into plant cells. Such repertoires include dozens of different T3Es, which can be grouped into superfamilies with diverse biochemical activities, plant interactor proteins, and virulence functions. The YopJ/HopZ/AvrBsT superfamily includes all HopZ effectors from P. syringae, and AvrBsT and related T3Es from Xanthomonas, some of which can suppress plant defense.In this work, we discuss the functional similarities between effectors of the YopJ superfamily present in several Xanthomonas and Pseudomonas strains, focusing on its virulence role in tomato and other host plants of agronomic relevance, and also present experimental evidence regarding the contribution of Pseudomonas effectors HopZla, HopZlc, and HopZ3 to virulence or avirulence in tomato plants. Working with the plant-bacteria interaction system comprising plants of tomato cultivars 'Moneymaker' and 'Rio Grande' and P. syringae pv. tomato strain DC3000, we show that neither HopZla nor HopZ3 are detected by the tomato immune system, or contribute to bacterial virulence. In contrast, we show that HopZlc is detected by the tomato immune system when expressed from strain DC3000, but contributes to virulence when expressed by its native strain.