Exploring the impact of Xanthomonas euvesicatoria effector XopL on ABA signaling and host cell metabolism.

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Xanthomonads are a genus of Gram-negative phytopathogens that cause disease in hundreds of economically important crop species worldwide. Xanthomonads are hemibiotrophic pathogens which spend a disproportionate amount of their life cycle living in/feeding off living plant tissue (biotrophic phase), but ultimately cause cell death during later stages of the infection (necrotrophic phase). Biotrophic growth phases require constant subversion of the plant immune system, and simultaneous conversion of the plant cell apoplast into a habitable environment. To address these challenges Xanthomonads utilize the type-III secretion system (T3SS) to inject bacterial-derived type III-secreted effector proteins (T3Es) directly into the host cytosol. T3Es are essential to pathogen virulence and it is generally understood that once inside, T3Es manipulate plant cell processes to support life in the apoplast. Intensive research into effector targets have revealed many of the plant processes that are vulnerable to pathogen attack, but exactly how these effector functions translate to changes in the apoplast where Xanthomonas actually resides are generally understudied. Going forward an understanding of Xanthomonas virulence requires that we link T3E function inside the cell to outcomes for the bacteria in the intracellular space.X. euvesicatoria (Xe) strain 85-10, the causal agent of bacterial spot disease on pepper and tomato, secretes 36 effector proteins, many of which are termed Xanthomonas outer proteins (Xops). One such protein, XopL, displays E3 ligase function in plants, where it hijacks the plant ubiquitylation cascade to modify plant substrate proteins. Preliminary work on XopL suggests that it might manipulate host cell metabolism by targeting a known ABA signaling component, ARIA (ARM REPEAT PROTEIN INTERACTING WITH ABF), for degradation. ARIA regulates the expression of genes important for the production of primary and secondary metabolites known to influence the success of pathogen growth in the apoplast. The goal of the proposed project is to utilize the XopL-ARIA interaction as a case study to determine whether the manipulation of the ABA signal cascade inside the cell can be linked to changes in the apoplast.