EcpA, an extracellular protease, is a specific virulence factor required by Xanthomonas oryzae pv. oryzicola but not by X. oryzae pv. oryzae in rice.
2012
Previously, 12 protease-deficient mutants of the Xanthomonas oryzae pv. oryzicola (Xoc) RS105 strain were recovered from a Tn5-tagged mutant library. In the current study, the Tn5 insertion site in each mutant was mapped. Mutations in genes encoding components of the type II secretion apparatus, cAMP regulatory protein, integral membrane protease subunit, S-adenosylmethionine decarboxylase proenzyme and extracellular protease (ecpAXoc
) either partially or completely abolished extracellular protease activity (ECPA) and reduced virulence in rice. Transcription of ecpAXoc
was induced in planta in all the mutants except RΔecpA. Complementation of RΔecpA with ecpAXoc in trans restored ECPA, virulence and bacterial growth in planta. Purified EcpA
Xoc
induced chlorosis- and necrosis-like symptoms similar to those induced by the pathogen when injected into rice leaves. Heterologous expression of ecpAXoc
conferred ECPA upon the vascular bacterium X. oryzae pv. oryzae (Xoo) and upon non-pathogenic Escherichia coli. Genetic analysis demonstrated that the C-terminal residues of EcpA in Xoo PXO99A and Xoc RS105 are different, and a frame shift in ecpAXoo
may explain the absence of EcpA activity in Xoo. Collectively, these results suggest that EcpA
Xoc
is a tissue-specific virulence factor for Xoc but not Xoo, although the two pathovars are closely related bacterial pathogens of rice.
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