Transcriptomic Insights Into Peppermint Adventitious Root Development Induced by Trichoderma Volatile Organic Compounds Under Salt Stress

Salt stress severely impacts a plant's root development. This study explores the role of volatile organic compounds (VOCs) from Trichoderma harzianum ST02 in enhancing adventitious root development of peppermint (Mentha × piperita), an important salt-tolerant medicinal plant, under salt stress. Peppermint seedlings were subjected to NaCl concentrations (0, 50, 100, and 150 mM) with or without exposure to T. harzianum ST02 VOCs. Morphological analyses revealed that VOCs significantly increased adventitious root numbers and total root length under salt stress, alleviating NaCl-induced damage. Gas chromatography-mass spectrometry (GC-MS) analysis found 3(2H)-furanone, dihydro-2-methyl, as a predominant component in T. harzianum ST02 VOCs. Transcriptomic analysis via RNA sequencing (RNA-seq) for four groups under different treatments identified 5589 differentially expressed genes (DEGs), with 298 DEGs specifically linked to VOCs exposure under 100 mM NaCl stress. Functional annotation indicated enrichment in pathways related to secondary metabolism and plant hormone signal transduction. VOCs modulated key genes, including those encoding ion transporters (e.g., SLAH2 and ABCG14), reactive oxygen species (ROS) scavenging (e.g., peroxidases), and cell wall-modifying enzymes (e.g., XTH). Notably, VOCs downregulated genes involved in abscisic acid (ABA) and ethylene biosynthesis (NCED3, ACS, and ACO), reducing stress signaling, while upregulating auxin (GH3.1) and gibberellin (GA2ox) metabolism genes, promoting root development. These findings suggest that T. harzianum ST02 VOCs enhance peppermint's salt tolerance by coordinately regulating hormone signaling, ion transport, and cell wall remodeling, thereby facilitating adventitious root development. Our work provides a molecular framework for utilizing beneficial microbes to improve plant resilience in saline environments.