Transcription factor CaMYB73 mediates greenhouse whitefly‐induced suppression of pepper defences

BACKGROUND: Although the herbivore manipulation of plant defences has been extensively studied, the molecular mechanisms by which the greenhouse whitefly Trialeurodes vaporariorum suppresses induced resistance in pepper and alters host-selection behaviour remain largely unclear. Here, we integrated behavioural, molecular, and biochemical analyses to elucidate how this pest manipulates pepper defence responses. RESULTS: In host-choice assays, whiteflies preferred to settle and oviposit on previously infested pepper plants rather than uninfested controls. Consistent with this behavioural preference, greenhouse whitefly infestation significantly down-regulated key genes involved in phenylpropanoid metabolism, particularly those associated with flavonoid pathways, and significantly reduced the accumulation of total phenolics and flavonoids. Using yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase reporter assays, we identified the R2R3-MYB transcription factor CaMYB73 as a negative regulator of CaPAL expression, which encodes the rate-limiting enzyme in phenylpropanoid metabolism. Mechanistically, CaMYB73 directly binds to a specific MYB-binding cis-element in the CaPAL promoter and represses CaPAL expression. Whitefly infestation strongly induced CaMYB73 expression, enabling the pest to attenuate phenylpropanoid defences through CaMYB73-mediated repression of CaPAL. Virus-induced silencing of CaMYB73 attenuated this suppression, restored the accumulation of total phenolics and flavonoids on whitefly attack, and significantly reduced whitefly settlement and oviposition. CONCLUSION: These findings reveal a novel mechanism by which greenhouse whiteflies exploit the CaMYB73-CaPAL regulatory module to compromise phenylpropanoid-mediated defences, thereby increasing host suitability for subsequent whitefly colonisation.