Abstract
This study aimed to dissect the function of the Isochorismatase Hydrolase (ICSH1) gene in Verticillium dahliae’s pathogenesis on potato. VdICSH1 was up-regulated in V. dahliae after induction with extracts from potato tissues. Its expression increased more in response to root extracts than to leaf and stem extracts. However, such expression in response to root extracts was not significantly different in the highly and weakly aggressive isolates tested. During infection of detached potato leaves, VdICSH1 expression increased significantly in the highly aggressive isolate compared to the weakly aggressive one. We generated icsh1 mutants from a highly aggressive isolate of V. dahliae and compared their pathogenicity with that of the original wild type strain. The analysis showed that this gene is required for full virulence of V. dahliae on potatoes. When we previously found differential accumulation of ICSH1 protein in favor of the highly aggressive isolate, as opposed to the weakly aggressive one, we had hypothesized that ICSH would interfere with the host’s defense SA-based signaling. Here, we measured the accumulation of both salicylic acid (SA) and jasmonic acid (JA) in potato plants inoculated with an icsh1 mutant in comparison with the wild type strain. The higher accumulation of bound SA in the leaves in response to the icsh1 mutant compared to the wild type confirms the hypothesis that ICSH1 interferes with SA. However, the different trends in SA and JA accumulation in potato in the roots and in the stems at the early infection stages compared to the leaves at later stages indicate that they are both associated to potato defenses against V. dahliae. The expression of members of the isochorismatase family in the icsh1 mutants compensate that of ICSH1 transcripts, but this compensation disappears in presence of the potato leaf extracts. This study indicates ICSH1’s involvement in V. dahliae’s pathogenicity and provides more insight into its alteration of the SA/JA defense signaling’s networking.
Highlights
Verticillium dahliae Kleb., a soil-borne hemi-biotrophic pathogen, causes wilt in more than 200 dicotyledonous plant species and is considered the primary causal agent of the potato early dying (PED) syndrome (Rowe and Powelson, 2002; Johnson and Dung, 2010)
There were no significant differences between responses of the highly and weekly aggressive isolates (Figure 1A)
As we initially predicted the possible role of this gene as a virulence factor using proteomics studies (El-Bebany et al, 2010), V. dahliae ICSH1 was found to reduce salicylic acid (SA) synthesis in cotton (Liu et al, 2014), and in potato tissues in the present study
Summary
Verticillium dahliae Kleb., a soil-borne hemi-biotrophic pathogen, causes wilt in more than 200 dicotyledonous plant species and is considered the primary causal agent of the potato early dying (PED) syndrome (Rowe and Powelson, 2002; Johnson and Dung, 2010). V. dahliae produces resting structures (microsclerotia) in the necrotic areas of infected tissues, which can sustain germination viability for long period of time up to 10 years or more in soil (Klosterman et al, 2009). Resistance to V. dahliae, mediated by the Ve1 gene, has been reported, but is limited to race 1 (Kawchuk et al, 2001; Fradin et al, 2009). Other studies reported potato defense genes induced in response to this infection (Derksen et al, 2013a)
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