The application of Trichoderma is a form of biological control that has been effective in combating Xanthomonas oryzae pv. oryzae, the causative agent of the devastating disease known as bacterial blight of rice. In this present study, four strains of Trichoderma, viz., T. paraviridescens (BDISOF67), T. erinaceum (BDISOF91), T. asperellum (BDISOF08), and T. asperellum (BDISOF09), were collected from the rice rhizosphere and used to test their potentiality in reducing bacterial blight. The expression patterns of several core defense-related enzymes and genes related to SA and JA pathways were studied to explore the mechanism of induced resistance by those Trichoderma strains. The results primarily indicated that all Trichoderma were significantly efficient in reducing the lesion length of the leaf over rice check variety (IR24) through enhancing the expression of core defense-related enzymes, such as PAL, PPO, CAT, and POD activities by 4.27, 1.77, 3.53, and 1.57-fold, respectively, over control. Moreover, the results of qRT-PCR exhibited an upregulation of genes OsPR1, OsPR10, OsWRKY45, OsWRKY62, OsWRKY71, OsHI-LOX, and OsACS2 after 24 h of inoculation with all tested Trichoderma strains. However, in the case of RT-PCR, no major changes in OsPR1 and OsPR10 expression were observed in plants treated with different Trichoderma strains during different courses of time. Collectively, Trichoderma induced resistance in rice against X. oryzae pv. oryzae by triggering these core defense-related enzymes and genes associated with SA and JA pathways.

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 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.

We previously identified rutin as part of potato root responses to its pathogen Verticillium dahliae. Rutin was directly toxic to the pathogen at doses greater than 160 μM, a threshold below which many V. dahliae pathogenicity-related genes were up-regulated. We identified and characterized a cupin domain-containing protein (VdQase) with a dioxygenase activity and a potential role in V. dahliae-potato interactions. The pathogenicity of VdQase knock-out mutants generated through Agrobacterium tumefasciens-mediated transformation was significantly reduced on susceptible potato cultivar Kennebec compared to wild type isolates. Fluorescence microscopy revealed a higher accumulation of flavonols in the stems of infected potatoes and a higher concentration of rutin in the leaves in response to the VdQase mutants as compared to wild type isolates. This, along with the HPLC characterization of high residual and non-utilized quercetin in presence of the knockout mutants, indicates the involvement of VdQase in the catabolism of quercetin and possibly other flavonols in planta. Quantification of Salicylic and Jasmonic Acids (SA, JA) in response to the mutants versus wild type isolates revealed involvement of VdQase in the interference with signaling, suggesting a role in pathogenicity. It is hypothesized that the by-product of dioxygenation 2-protocatechuoylphloroglucinolcarboxylic acid, after dissociating into phloroglucinol and protocatechuoyl moieties, becomes a starting point for benzoic acid and SA, thereby interfering with the JA pathway and affecting the interaction outcome. These events may be key factors for V. dahliae in countering potato defenses and becoming notorious in the rhizosphere.

KdgR has been reported to negatively regulate the genes involved in degradation and metabolization of pectic acid and other extracellular enzymes in soft-rotting Erwinia spp. through direct binding to their promoters. The possible involvement of a KdgR orthologue in virulence by affecting the expression of extracellular enzymes in Xanthomonas oryzae pv. oryzae, the causal agent of rice blight disease, was examined by comparing virulence and regulation of extracellular enzymes between the wild type (WT) and a strain carrying a mutation in putative kdgR (ΔXoo0310 mutant). This putative kdgR mutant of X. oryzae pv. oryzae showed increased pathogenicity on rice without affecting the regulation of extracellular enzymes, such as amylase, cellulase, xylanase, and protease. However, the mutant carrying a mutation in an ortholog of xpsL, which encodes the functional secretion machinery for the extracellular enzymes, showed a dramatic decrease in pathogenicity on rice. Both mutants of kdgR and of xpsL orthologs showed higher expression of two major hrp regulatory genes, hrpG and hrpX, and the genes in the hrp operons when grown in hrp-inducing medium. Thus, both genes were shown to be involved in repression of hrp genes. The kdgR ortholog was thought to suppress virulence mainly by repressing the expression of hrp genes without affecting the expression of extracellular enzymes, unlike findings for the kdgR gene in soft-rotting Erwinia spp. On the other hand, xpsL was confirmed to be involved in virulence by promoting the secretion of extracellular enzymes in spite of repressing the expression of the hrp genes.