Overexpression of Cotton Salicylic Acid Carboxyl Methyltransferase Genes <i>GhSAMT1</i> and <i>GhSAMT3</i> 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 <i>SAMT</i>-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 <i>Apolygus lucorum</i> and <i>Helicoverpa armigera</i> highlighted upregulation of both jasmonic acid and SA pathway genes, specifically three <i>SAMT</i> 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 <i>Nicotiana tabacum</i> overexpressing <i>GhSAMT1</i> or <i>GhSAMT3</i> emitted high MeSA levels, attracting three important parasitoids (<i>Peristenus spretus</i>, <i>Telenomus remus</i>, and <i>Trichogramma ostriniae</i>). These findings highlight SAMT's role in MeSA-mediated indirect defenses, offering a sustainable strategy for pest control via volatile manipulation.