Biosynthesis of Amino Acids in Xanthomonas oryzae pv. oryzae Is Essential to Its Pathogenicity

Abstract

Xanthomonas oryzae pv. oryzae (Xoo) is the causal agent of rice bacterial blight disease, which causes a large reduction in rice production. The successful interaction of pathogens and plants requires a particular nutrient environment that allows pathogen growth and the initiation of both pathogen and host responses. Amino acid synthesis is essential for bacterial growth when bacteria encounter amino acid-deficient environments, but the effects of amino acid synthesis on Xoo pathogenicity are unclear. Here, we systemically deleted the essential genes (leuB, leuC, leuD, ilvC, thrC, hisD, trpC, argH, metB, and aspC) involved in the synthesis of different amino acids and analyzed the effects of these mutations on Xoo virulence. Our results showed that leucine, isoleucine, valine, histidine, threonine, arginine, tryptophan, and cysteine syntheses are essential to Xoo infection. We further studied the role of leucine in the interaction between pathogens and hosts and found that leucine could stimulate some virulence-related responses and regulate Xoo pathogenicity. Our findings highlight that amino acids not only act as nutrients for bacterial growth but also play essential roles in the Xoo and rice interaction.Microorganisms 2019, 7, 693 2 of 12 regulates intracellular signaling pathways but also has important effects on protein synthesis and immunity in plants [3]. Disruption of leucine synthesis influences iron homeostasis and thus attenuates the virulence of the fungus Cryptococcus neoformans [9]. Another report has also shown that leucine synthesis is essential to the growth of Acidovorax citrulli in planta [10]. These findings suggest that amino acid synthesis is important for bacteria and fungi to successfully infect hosts.Xanthomonas oryzae pv. oryzae (Xoo) is a Gram-negative bacterium and the causal agent of rice bacterial blight disease, which causes a large reduction in rice production around the world. Plant diseases are caused by the interaction of pathogens and plants in a particular nutrient environment, which is dependent on the interaction between plant and pathogen factors. Although a previous study has shown that histidine can affect the pathogenicity of Xanthomonas oryzae pv. oryzicola (Xoc) [11], the roles of amino acids in the Xoo-rice interaction remain unclear.In this study, we identified and functionally characterized the essential genes for Xoo amino acid synthesis. We found that synthesis of leucine, isoleucine, valine, histidine, threonine, arginine, tryptophan, and cysteine is important for Xoo infection. We also analyzed the roles of branched-chain amino acids (BCAAs), especially leucine, in the Xoo-rice interaction in detail and found that leucine can regulate diverse pathways to influence Xoo virulence. Our data indicate that amino acids are not only essential nutrients for Xoo, but also regulate virulence-related pathways to influence its infection processes. Our study establishes a solid link between primary metabolism and bacterial pathogenicity and provides new ideas for protecting ...

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