A single amino acid substitution in PthA of <Emphasis Type="Italic">Xanthomonas axonopodis</Emphasis> pv. <Emphasis Type="Italic">citri</Emphasis> altering canker formation on grapefruit leaves |
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Authors: | Hsin-Cheng Lin Mu-Kuei Chu Yuang-Chuen Lin Wen-Ling Deng Hsiang Chang Shih-Tien Hsu Kuo-Ching Tzeng |
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Institution: | (1) Department of Biotechnology, Chung Chou Institute of Technology, Changhua, 51003, Taiwan;(2) Department of Biological Science and Technology, Chung Hwa University of Medical Technology, Tainan County, 71703, Taiwan;(3) Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan;(4) Department of Plant Pathology, National Chung-Hsing University, Taichung, 40227, Taiwan;(5) Department of Biotechnology, Asia University, Taichung County, 41354, Taiwan |
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Abstract: | The typical citrus canker lesions produced by Xanthomonas axonopodis pv. citri are erumpent, callus-like, with water-soaked margins. Three novel atypical symptom-producing variants of X. axonopodis pv. citri were described recently in Taiwan. Only the variant designated as Af type produces typical erumpent canker lesions on Mexican lime (Citrus aurantifolia) but induces flat necrotic with water-soaked margin lesions on grapefruit leaves (C. paradisi). Two homologous pthA were cloned and characterized from strains XW19 (a typical canker lesion producing strain) and XW47 (a strain of Af type). The pthA homolog from XW19 was transformed into XW47. The transformant of XW47 induced typical erumpent canker lesions on grapefruit
leaves. Sequence analyses of transformants XW19 and XW47 revealed over 99% homology in nucleotide and deduced amino acid sequences
compared with pthA homologs deposited in GenBank. The amino acid residues located at positions 49, 286, 742 and 767 of PthA were different between
XW47 and XW19. The PthA mutants with a single amino acid substitution at each of these four positions were constructed by
site-directed mutagenesis. Modified PthA (S286P) from XW47 in transformant 47SP induced erumpent canker lesions on grapefruit
leaves, whereas another modified PthA (P286S) from XW19 in transformant 47PS only induced flat necrotic lesions. These results
suggested that a single amino acid substitution from either serine to proline or proline to serine at position 286 of PthA
can alter canker formation by X. axonopodis pv. citri on grapefruit leaves. |
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