Integrated transcriptomics and metabolomics analyses revealed mechanisms of Trichoderma harzianum-induced resistance to downy mildew in grapevine

Abstract

Downy mildew, caused by Plasmopara viticola (P. viticola, Berk. & M. A. Curtis; Berl. & De Toni), represents a major threat to the grapevine industry in China. Although Trichoderma harzianum has been identified as an effective biocontrol agent, the molecular mechanisms by which it modulates grapevine resistance to P. viticola remain poorly understood. This study utilized Vitis vinifera cv. ‘Cabernet Sauvignon’ grape leaves as experimental material, with treatments consisting of inoculation with sterile water (control) or T. harzianum, followed by P. viticola inoculation 24 h later. Transcriptomic and metabolomic analyses were conducted at 0, 1, and 5 days post-inoculation. A total of 13,292 distinct genes exhibiting differential expression were identified, and the KEGG pathway enrichment analysis indicated that these genes were primarily associated with plant hormone signal transduction, plant-pathogen interactions, phenylpropanoid metabolism, and flavonoid synthesis. Notably, T. harzianum treatment significantly upregulated key genes encoding phenylalanine ammonia lyase (PAL), 4-coumarate-CoA ligase (4CL), and flavonoid 3-hydroxylase (F3H), leading to enhanced synthesis of lignin and flavonoids, which augmented grapevine resistance to P. viticola infection. Additionally, metabolomic analysis demonstrated a substantial accumulation of various metabolites, including flavonoids (e.g., luteolin) and phenolic acids (e.g., caffeic acid and ferulic acid), in response to T. harzianum treatment. These metabolites are likely involved in reinforcing the cell wall and inhibiting pathogen spread, thereby contributing to enhanced disease resistance. Correlation analysis further revealed a significant positive association between flavonoid compounds and defense-related gene expression, suggesting that T. harzianum enhances grapevine resistance to downy mildew through modulation of secondary metabolite accumulation and related gene expression. Collectively, these findings provide new insights into the complex regulatory mechanisms by which T. harzianum enhances grapevine resistance to P. viticola, offering a theoretical framework for employing biological control strategies to improve grapevine disease resistance and inform breeding programs aimed at developing downy mildew-resistant cultivars.