Trichoderma erinaceum Bio-Priming Modulates the WRKYs Defense Programming in Tomato Against the Fusarium oxysporum f. sp. lycopersici (Fol) Challenged Condition

Abstract

The beneficial association and interaction of rhizocompetent microorganisms are widely used for plant biofertilization and amelioration of stress-induced damage in plants. To explore the regulatory mechanism involved in plant defense while associating with beneficial microbial species, and their interplay when co-inoculated with pathogens, we evaluated the response of tomato defense-related <i>WRKY</i> gene transcripts. The present study was carried out to examine the qRT-PCR-based relative quantification of differentially expressed defense-related genes in tomato (<i>Solanum lycopersicum</i> L.; variety S-22) primed with <i>Trichoderma erinaceum</i> against the vascular wilt pathogen (<i>Fusarium oxysporum</i> f. sp. <i>lycopersici</i>). The tissue-specific and time-bound expression profile changes under the four different treatments "(unprimed, <i>Fol</i> challenged, <i>T. erinaceum</i> primed and <i>Fol</i>+ <i>T. erinaceum</i>)" revealed that the highest upregulation was observed in the transcript profile of <i>SlWRKY31</i> (root) and <i>SlWRKY37</i> (leaf) in <i>T. erinaceum</i> bioprimed treated plants at 24 h with 16.51- and 14.07-fold increase, respectively. In contrast, <i>SlWRKY4</i> showed downregulation with the highest repression in <i>T. erinaceum</i> bioprimed root (24 h) and leaf (48 h) tissue samples with 0.03 and 0.08 fold decrease, respectively. Qualitative expression of PR proteins (chitinases and glucanases) was found elicited in <i>T. erinaceum</i> primed plants. However, the antioxidative activity of tomato superoxide dismutase and catalase increased with the highest upregulation of <i>SOD</i> and <i>SlGPX1</i> in <i>Fol + T. erinaceum</i> treatments. We observed that these expression changes were accompanied by 32.06% lesser H₂O₂ production in <i>T. erinaceum</i> bioprimed samples. The aggravated defense response in all the treated conditions was also reflected by an increased lignified stem tissues. Overall, we conclude that <i>T. erinaceum</i> bio-priming modulated the defense transcriptome of tomato after the <i>Fol</i> challenged conditions, and were accompanied by enhanced accumulation of defense-related <i>WRKY</i> transcripts, increased antioxidative enzyme activities, and the reinforcements through a higher number of lignified cell layers.