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 WRKY gene transcripts. The present study was carried out to examine the qRT–PCR-based relative quantification of differentially expressed defense-related genes in tomato (Solanum lycopersicum L.; variety S-22) primed with Trichoderma erinaceum against the vascular wilt pathogen (Fusarium oxysporum f. sp. lycopersici). The tissue-specific and time-bound expression profile changes under the four different treatments “(unprimed, Fol challenged, T. erinaceum primed and Fol+ T. erinaceum)” revealed that the highest upregulation was observed in the transcript profile of SlWRKY31 (root) and SlWRKY37 (leaf) in T. erinaceum bioprimed treated plants at 24 h with 16.51- and 14.07-fold increase, respectively. In contrast, SlWRKY4 showed downregulation with the highest repression in T. erinaceum 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 T. erinaceum primed plants. However, the antioxidative activity of tomato superoxide dismutase and catalase increased with the highest upregulation of SOD and SlGPX1 in Fol + T. erinaceum treatments. We observed that these expression changes were accompanied by 32.06% lesser H2O2 production in T. erinaceum bioprimed samples. The aggravated defense response in all the treated conditions was also reflected by an increased lignified stem tissues. Overall, we conclude that T. erinaceum bio-priming modulated the defense transcriptome of tomato after the Fol challenged conditions, and were accompanied by enhanced accumulation of defense-related WRKY transcripts, increased antioxidative enzyme activities, and the reinforcements through a higher number of lignified cell layers.
Highlights
Microbial bio-priming represents an adaptive strategy to improve the defensive capacity of plants that result in increased resistance/stress tolerance, and/or a more aggravated defense response against the stress challenged conditions
The results suggested that SlWRKY31 and SlWRKY37 function as a positive regulator and SlWRKY4 as a negative regulator of plant defense programmed against the Fol challenged condition with a more aggressive defense response in Trichoderma pre-primed plants compared to non-primed plants
Microbial priming with Trichoderma spp. results into transcriptional regulation of defense-related genes with altered expression level
Summary
Microbial bio-priming represents an adaptive strategy to improve the defensive capacity of plants that result in increased resistance/stress tolerance, and/or a more aggravated defense response against the stress challenged conditions. The rhizocompetent nature of Trichoderma spp. allows it to colonize roots, stimulates the plant immune system (induced systemic resistance; ISR), and pre-activation (priming) of the molecular mechanisms of defense against several potent phytopathogens (Hermosa et al, 2012; Pieterse et al, 2014; Martínez-Medina et al, 2017). Colonization of this beneficial fungi promotes plant growth and ameliorates the host plants against various abiotic and biotic stresses (Brotman et al, 2013; Zhang et al, 2016; Fu et al, 2017). Studies revealed that besides the W-box-specific DNA binding, WRKY specific stimulus-response is facilitated by other essential components that regulate the biological function of different
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