An HrpB-dependent but type III-independent extracellular aspartic protease is a virulence factor of Ralstonia solanacearum

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Title
An HrpB-dependent but type III-independent extracellular aspartic protease is a virulence factor of Ralstonia solanacearum
Author(s)
Y Jeong; H Cheong; O Choi; Jung-Kyu Kim; Y Kang; J Kim; S Lee; Serry Koh; Jae Sun Moon; I Hwang
Bibliographic Citation
Molecular Plant Pathology, vol. 12, no. 4, pp. 373-380
Publication Year
2011
Abstract
The host specificity of Ralstonia solanacearum, the causal organism of bacterial wilt on many solanaceous crops, is poorly understood. To identify a gene conferring host specificity of the bacterium, SL341 (virulent to hot pepper but avirulent to potato) and SL2029 (virulent to potato but avirulent to hot pepper) were chosen as representative strains. We identified a gene, rsa1, from SL2029 that confers avirulence to SL341 in hot pepper. The rsa1 gene encoding an 11.8-kDa protein possessed the perfect consensus hrp(II) box motif upstream of the gene. Although the expression of rsa1 was activated by HrpB, a transcriptional activator for hrp gene expression, Rsa1 protein was secreted in an Hrp type III secretion-independent manner. Rsa1 exhibited weak homology with an aspartic protease, cathepsin D, and possessed protease activity. Two specific aspartic protease inhibitors, pepstatin A and diazoacetyl-d,l-norleucine methyl ester, inhibited the protease activity of Rsa1. Substitution of two aspartic acid residues with alanine at positions 54 and 59 abolished protease activity. The SL2029 rsa1 mutant was much less virulent than the wild-type strain, but did not induce disease symptoms in hot pepper. These data indicate that Rsa1 is an extracellular aspartic protease and plays an important role for the virulence of SL2029 in potato.
ISSN
1464-6722
Publisher
Wiley
DOI
http://dx.doi.org/10.1111/j.1364-3703.2010.00679.x
Type
Article
Appears in Collections:
Division of Research on National Challenges > Plant Systems Engineering Research > 1. Journal Articles
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