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Xanthomonas oryzae pv. oryzae XKK.12 Contains an AroQ_γ Chorismate Mutase That Is Involved in Rice Virulence

First, second, and fourth authors: Bacteriology Group, International Centre for Genetic Engineering & Biotechnology, Trieste, Italy; third and fourth authors: Plant Bacteriology Group, International Centre for Genetic Engineering & Biotechnology, Biosafety Outstation, Ca'Tron, Treviso, Italy.

Chorismate mutase (CM) is a key enzyme in the shikimate pathway which is responsible for the synthesis of aromatic amino acids. There are two classes of CMs, AroQ and AroH, and several pathogenic bacteria have been reported to possess a subgroup of CMs designated AroQ_γ. These CMs are usually exported to the periplasm or outside the cell; in a few cases, they have been reported to be involved in virulence and their precise role is currently unknown. Here, we report that the important rice pathogen Xanthomonas oryzae pv. oryzae XKK.12 produces an AroQ_γ CM which we have purified and characterized from spent supernatants. This enzyme is synthesized in planta and X. oryzae pv. oryzae knock-out mutants are hypervirulent to rice. The role of this enzyme in X. oryzae pv. oryzae rice virulence is discussed.