Transcriptomic Analysis Reveals the Regulatory Network of Allyl Isothiocyanate Induced Insect Defense in Pakchoi

Allyl isothiocyanate (AITC), a sulfur-containing volatile from the cruciferous glucosinolate-myrosinase hydrolysis, the core reaction of the "mustard oil bomb", acts as an antimicrobial, insecticidal, and airborne signaling molecule. In this study, two treatments were established: direct fumigation with AITC (Group D) and plant-to-plant aerial chemical communication (Group T) in pakchoi, and RNA-seq, RT-qPCR, glucosinolate (GSL)/isothiocyanate (ITC) quantification, and Spodoptera litura feeding assays were used to investigate AITC-induced insect resistance. Transcriptomic analysis revealed that differentially expressed genes (DEGs) were significantly enriched in plant hormone signal transduction and phenylpropanoid biosynthesis pathways. Metabolically, AITC effectively promoted the conversion of GSL to ITC, resulting in higher total ITC content in all treatment groups compared to the control, following a time-dependent accumulation pattern. Spodoptera litura larvae displayed reduced feeding preference for AITC-treated pakchoi, which was negatively correlated with ITC levels. This study reveals the key regulatory mechanism by which AITC enhances secondary metabolism and produces volatile metabolites for insect defense, probably through activating a signaling network centered on jasmonic acid (JA) and synergizing with other hormones. It also confirms AITC's role in airborne early warning and plant-to-plant signal transmission, providing theoretical foundations and practical references for developing green pest control technologies based on plant volatile metabolites, such as AITC. However, the specific sensory receptors mediating AITC-induced plant airborne immunity, the detailed processes of signal transmission between plants, and the interactive networks with other defense pathways still require further in-depth exploration.