Overexpression of Cotton Salicylic Acid Carboxyl Methyltransferase Genes GhSAMT1 and GhSAMT3 Enhances MeSA-Mediated Parasitoid Recruitment.

Methyl salicylate (MeSA), synthesized from salicylic acid (SA) by salicylic acid carboxyl methyltransferase (SAMT), plays a critical role in plant-insect-environment interactions. This study investigates SAMT-mediated MeSA biosynthesis in cotton and its manipulation for pest control. Volatile analyses showed MeSA emissions of 50.38 and 45.68 ng·plant-1 · 4 h-1 in herbivore- and SA-treated cotton, respectively. Transcriptomic analysis of cotton plants simultaneously infested with Apolygus lucorum and Helicoverpa armigera highlighted upregulation of both jasmonic acid and SA pathway genes, specifically three SAMT genes potentially involved in SA-dependent MeSA emission. In vitro and in vivo functionally characterized that four recombinant proteins (GhSAMT1, GhSAMT2, GhSAMT3/GbSAMT3, and GaSAMT3) efficiently convert SA into MeSA. Transgenic Nicotiana tabacum overexpressing GhSAMT1 or GhSAMT3 emitted high MeSA levels, attracting three important parasitoids (Peristenus spretus, Telenomus remus, and Trichogramma ostriniae). These findings highlight SAMT's role in MeSA-mediated indirect defenses, offering a sustainable strategy for pest control via volatile manipulation.