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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #283335
Title: EcpA, an extracellular protease, is a specific virulence factor required by Xanthomonas oryzae pv. oryzicola but not by X. oryzae pv. oryzae in rice

Author
item ZOU, HUA-SONG - Shanghai Jiaotong University
item SONG, XUE - Shanghai Jiaotong University
item ZOU, LI-FANG - Shanghai Jiaotong University
item CHEN, GONG-YOU - Shanghai Jiaotong University
item YUAN, LIANG - Nanjing Agricultural University
item GUO, WEI - Nanjing Agricultural University
item CHE, YI-ZHOU - Nanjing Agricultural University
item ZHAO, WEN-XIANG - Nanjing Agricultural University
item Duan, Ping

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2012
Publication Date: 7/1/2012
Citation: Zou, H., Song, X., Zou, L., Chen, G., Yuan, L., Guo, W., Che, Y., Zhao, W., Duan, Y. 2012. EcpA, an extracellular protease, is a specific virulence factor required by Xanthomonas oryzae pv. oryzicola but not by X. oryzae pv. oryzae in rice. American Phytopathological Society Annual Meeting. 158:2372-2383.

Interpretive Summary: Xanthomonas oryzae pv. oryzicola (Xoc) causes bacterial leaf streak (BLS), an emerging and destructive disease in rice worldwide. Identification of key virulence factors is necessary for understanding the pathogenesis of Xoc. In this study, a Tn5-tagged mutant library of Xoc strain RS105 was screened on rice and the insertion site of the Tn5 tag in each mutant was mapped. Mutations in genes encoding components of the type II secretion apparatus (which transports proteins across the inner and outer cell membranes of Gram negative bacteria) either partially or completely abolished extracellular protease activity (ECPA) and reduced virulence in rice. Proteases are a large family of enzymes that digest the peptide bonds in proteins thus breaking them down into their constituent monomers. Transcription of extracellular protease (ecpAXoc) was induced in planta in all the mutants except R'ecpA and complementation of R'ecpA with the ecpAXoc in trans restored ECPA, virulence and bacterial growth. Expression of ecpAXoc in non-pathogenic E. coli and the vascular bacterium X. oryzae pv. oryzae (Xoo) established ECPA. Sequence differences in the C-terminus and a frame shift mutation in ecpAXoo may explain the lack of endogenous activity. These results suggest that EcpAXoc is a tissue-specific virulence factor for Xoc but not Xoo, although both strains are closely-related bacterial pathogens of rice.

Technical Abstract: Previously, twelve protease-deficient mutants of 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 R'ecpA. Complementation of R'ecpA with the ecpAXoc in trans restored ECPA, virulence and bacterial growth in planta. Purified EcpAXoc induced chlorosis- and necrosis-like symptoms similar to the pathogen when injected into rice leaves. Heterologous expression of ecpAXoc conferred ECPA to the vascular bacterium X. oryzae pv. oryzae (Xoo) and to nonpathogenic E. coli, respectively. 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 EcpAXoc is a tissue-specific virulence factor for Xoc but not Xoo, although both pathovars are closely-related bacterial pathogens of rice.