A plant virus, TYLCV, up-regulates an endocrine oxylipin signal in its insect vector, Bemisia tabaci, via the viral C2 virulence factor for viral transmission

Abstract Background Tomato yellow leaf curl virus (TYLCV) is transmitted by Bemisia tabaci through a circulative and replicative pathway and must overcome vector immune defenses to achieve efficient transmission. Oxylipins are important regulators of insect immunity, in which eicosanoids generally promote antiviral responses whereas C18 epoxyoctadecamonoenoic acids (EpOMEs) act as immune suppressors. Although manipulation of insect immunity by plant viruses has been increasingly recognized, the molecular mechanisms by which TYLCV reshapes vector physiology to establish a permissive infection state remain poorly understood. Methodology TYLCV infection and localization in B. tabaci were analyzed using fluorescence in situ hybridization (FISH), immunofluorescence assays (IFA), and quantitative PCR. Oxylipin functions were examined through oral delivery of prostaglandins, EpOMEs, pathway inhibitors, and lipid analogs. EpOME levels were quantified by LC–MS/MS. Candidate genes involved in eicosanoid and EpOME biosynthesis or degradation were predicted through bioinformatic and phylogenetic analyses and functionally evaluated using RNA interference (RNAi). Intestinal apoptosis was assessed using TUNEL and cleaved caspase-3 immunostaining. Immune-associated genes and viral determinants were investigated through RT-qPCR and gene-specific RNAi, including silencing of all six TYLCV genes. Results TYLCV progressively accumulated in the intestine of B. tabaci and significantly altered fatty acid metabolism. Two oxylipin pathways exerted antagonistic effects on viral accumulation. Prostaglandin E₂ (PGE₂) and its biosynthetic machinery, including BtPLA2-A, BtPLA2-C, Bt-PGES2, and Bt-PGE2R, functioned as antiviral regulators, whereas both EpOME isomers (9,10- and 12,13-EpOME) promoted viral accumulation. TYLCV infection elevated EpOME levels more than two-fold and transcriptionally favored EpOME accumulation by inducing Bt-CYP6 while suppressing Bt-sEH2 and Bt-sEH3 . Pharmacological and RNAi analyses confirmed Bt-CYP6 as an EpOME-associated synthase and Bt-sEH2/3 as degradation-associated genes. EpOME promoted intestinal apoptosis and selectively regulated immune-associated genes, inducing proviral factors including defensin and cathepsins while suppressing antiviral factors such as knottin and PGRP. Comparison of TYLCV strains revealed that the more virulent TYLCV-IL induced stronger EpOME signaling and apoptosis than TYLCV-Mld. Among all viral genes, only TYLCV-C2 controlled host EpOME machinery; silencing C2 abolished Bt-CYP6 induction and restored Bt-sEH2/3 expression, while exogenous EpOME rescued viral accumulation. Conclusion TYLCV exploits vector oxylipin signaling to establish a permissive physiological state in B. tabaci . Through the viral C2 factor, TYLCV shifts host signaling from an antiviral eicosanoid-dominant state toward a proviral EpOME-dominant state, thereby promoting apoptosis, reshaping immune responses, and enhancing viral accumulation and transmission potential.