Mutational analysis of type III effector genes from <Emphasis Type="Italic">Xanthomonas citri</Emphasis> subsp. <Emphasis Type="Italic">citri</Emphasis> |
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Authors: | Jose Francisco L Figueiredo Gerald V Minsavage James H Graham Frank F White Jeffrey B Jones |
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Institution: | (1) Plant Pathology Department, University of Florida, Gainesville, FL, USA;(2) Citrus Research and Education Center (CREC), University of Florida, Lake Alfred, FL, USA;(3) Plant Pathology Department, Kansas State University, Manhattan, KS, USA |
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Abstract: | Xanthomonas citri subsp. citri, the causal agent of citrus canker, relies extensively on a type III secretion system for infection by delivering type III
effectors into host cells. In the genus Xanthomonas, two major regulators, HrpG and HrpX, are involved in the expression of genes encoding the type III secretion system. Twenty-three
candidate type III effectors were identified as targets for analysis. The involvement in pathogenicity of 20 candidate effector
genes in X. citri strain 306 (Xcc-306) was investigated using site-directed mutagenesis. Pathogenicity assays in grapefruit of 19 genes using
site-directed mutagenesis revealed that none of the mutants demonstrated to have reduced ability to cause canker disease.
A mutation in the TAL effector pthA4
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resulted in loss of hypertrophy although no changes were observed in bacterial growth in leaves. Mutations in hrpG, hrpX, or hrpA genes displayed a complete loss of pathogenicity. Moreover, all mutants maintained the ability to trigger a hypersensitive
response (HR) in non-host tomato. In contrast to previous studies, hrpG
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, hrpX
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and hrpA
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mutants also retained the ability to elicit an HR in tomato, indicating the presence of an Hrp independent elicitor in Xcc-306. |
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Keywords: | |
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