|WEI, HAI-LEI - Cornell University - New York|
|CHAKRAVARTHY, SUMA - Cornell University - New York|
|MATHIEU, JOHANNES - Boyce Thompson Institute|
|HELMANN, TYLER - Cornell University - New York|
|MARTIN, GREGORY - Boyce Thompson Institute|
|COLLMER, ALAN - Cornell University - New York|
Submitted to: Cell Host and Microbe
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2015
Publication Date: 6/10/2015
Citation: Wei, H., Chakravarthy, S., Mathieu, J., Helmann, T.C., Stodghill, P., Swingle, B.M., Martin, G.B., Collmer, A. 2015. Pseudomonas syringae pv. Tomato DC3000 Type III secretion effector polymutants reveal an interplay between hopAD1 AvrPtoB. Cell Host and Microbe. 17(6):752-62.
Interpretive Summary: Plant pathogens inject multiple effector proteins into plant cells to suppress the plant immune response and enable the pathogens to cause disease. In most cases, the function of individual effectors is not known or cannot be detected because their interactions with plant systems is masked by the action of other effectors. To address these issues, a model plant pathogen (Pseudomonas syringae) was modified by deleting all of its known effector genes. This modified pathogen was no longer able to cause disease or plant cell death. Further analysis of this modified pathogen enabled the discovery of HopAD1 effector function and revealed a new function for the well-studied effector, AvrPtoB. This work demonstrates the utility of the engineered pathogen strain for analyzing the function of pathogen effectors in plants. This is likely to have a large impact on the ways that scientists study the molecular details of plant interactions with bacteria, fungi, and plant eating insects. Additionally, this work led to the discovery of new details regarding the mechanisms that bacteria use to overcome plant immunity, which informs our understanding of how to implement plant resistance to control disease in crops.
Technical Abstract: The model pathogen Pseudomonas syringae pv. tomato DC3000 suppresses the two-tiered innate immune system of plants by injecting a complex repertoire of effector proteins into host cells via the type III secretion system. The model effector AvrPtoB has multiple domains and plant protein interactors in both tiers of immunity. A functionally effectorless Pst DC3000 polymutant lacking 36 effectors was constructed, sequence confirmed, and used to explore interplay among effectors in minimalized repertoires. HopAD1 was found to elicit in the model plant Nicotiana benthamiana an immunity-associated cell death that was suppressed partially by native AvrPtoB and completely by AvrPtoBM3, which has site-specific mutations disrupting its E3 ubiquitin ligase domain and the two known domains for interacting with immunity-associated kinases. AvrPtoBM3 also gained the ability to interact strongly in a yeast two-hybrid system with immunity-associated kinase MKK2, whose production is needed for HopAD1-dependent cell death. The use of the native pathogen with reduced subsets of effectors has revealed new virulence activities for AvrPtoB and establishes an optimum system for studying effector interplay.