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The PdeR-TriP interaction mediates a novel c-di-GMP signaling pathway to regulate virulence of Xanthomonas oryzae pv. oryzae
H. Li (1), F. Tian (1), D. Xue (1), H. Chen (1), X. Yuan (2), C. H. Yang (2), C. HE (1). (1) Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China; (2) Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI, U.S.A.

PdeK/PdeR, the two-component system (TCS), was previously shown to regulate the virulence of the rice bacterial blight pathogen <i>Xanthomonas oryzae </i>pv. <i>oryzae </i>(Xoo). The response regulator PdeR harbors phosphodiesterase (PDE) activity to degrade bacterial second messenger cyclic di-GMP. To understand the downstream signaling pathway mediated by PdeR, we started with looking for its interacting partners in Xoo strain PXO99<sup>A</sup>. Here, we identified a response regulator PXO_04421, named as TriP, as an interactor of PdeR. Yeast two-hybrid (Y2H) and GST pull-down assays confirmed the PdeR-Trip interaction. Interestingly, the interaction was inhibited by high concentration of c-di-GMP. Virulence assays demonstrated that the <i>triP </i>mutant caused shorter lesion length on rice leaves than the wild type, and its ability to progress through the xylem tissue was also impaired. Moreover, both the <i>pdeR </i>and the <i>triP </i>single mutant produced less exopolysaccharide (EPS), while the <i>pdeR/triP </i>double mutant produced similar level of EPS with that of the <i>triP </i>mutant. These results indicated that TriP and PdeR are functionally related in regulation of bacterial virulence. Additionally, RNA-seq analysis revealed a considerable overlap in the up-regulated genes in the two single mutants, which further implied that TriP might mediate a part of the PdeR-mediated signaling in Xoo.

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