Cotton Recruits Soil‐Derived Delftia tsuruhatensis to Suppress Aphid Detoxification Via Salicylic Acid‐Mediated Defense

ABSTRACT The synergistic defense between microorganisms and plants holds significant ecological importance in resisting pest attacks. Herbivorous insects pose a significant threat to global agriculture. While plants deploy defense hormones like jasmonic acid (JA) and salicylic acid (SA), the role of beneficial microbes in enhancing these defenses remains underexplored. This study unveils a novel tripartite interaction in which cotton actively mobilizes the soil‐derived bacterium Delftia tsuruhatensis to roots and leaves upon aphid attack, reshaping its microbiome for defense. Following aphid infestation, the abundance of D. tsuruhatensis was increased significantly in both roots and leaves. Inoculation of cotton with D. tsuruhatensis significantly reduced aphid fitness, inhibiting phloem feeding, decreasing survival, prolonging nymphal development, and impairing reproduction. Mechanistically, we found that D. tsuruhatensis activates the host plant's SA signaling pathway. This plant‐mediated response, in turn, effectively suppresses the expression of a key aphid detoxification gene, UGT2B17 ( UDP‐glucosyltransferase 2B17 ), compromising the insect's ability to metabolize plant defenses. Furthermore, the combination of D. tsuruhatensis and RNAi‐mediated silencing of UGT2B17 synergistically enhanced aphid mortality. Our results elucidate a sophisticated defense strategy wherein the host plant leverages a beneficial microbe to augment its innate immunity through cross‐kingdom gene regulation, ultimately disarming the pest's detoxification system.