Manipulation of tomato root cells by Brg11, a TALE-like protein of the bacterial pathogen Ralstonia solanacearum

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Plant-pathogenic bacteria inject effector proteins into host cells that manipulate key cellular processes to promote disease. Thus, effectors can serve as molecular probes to uncover yet unknown key components of plant-microbe interactions. We study Brg11, an effector protein that is present in numerous strains of the broad-host pathogen Ralstonia solanacearum. Brg11 was found to transcriptionally activate expression of arginine decarboxylase (ADC) genes across all of its host plants, suggesting that ADC proteins promote virulence of R. solanacearum. ADC proteins are rate-limiting enzymes in the biosynthesis of polyamines (PAs), a class of metabolites with two or more amino groups that exist throughout all three kingdoms of life. While R. solanacearum was found to boost host PA levels, strains of the bacterial pathogen Pseudomonas syringae deliberately reduce host PA levels. Notably, elevated PA level inhibit in planta growth of P. syringae but not of R. solanacearum. These observations suggest that R. solanacearum Brg11 induces elevated PA levels in host cells to inhibit growth of microbial niche competitors. We will investigate PA-induced changes in host cells at the cellular and molecular level. Overall, these studies will provide a better understanding of how plant PA levels affect host-microbe interactions.