Vitellogenin from planthopper oral secretion acts as a novel effector to impair plant defenses

Vitellogenin (Vg) is a well-known nutritious protein involved in reproduction in nearly all oviparous animals, including insects. Recently, Vg has been detected in saliva proteomes of several piercing-sucking herbivorous arthropods, including the small brown planthopper (Laodelphax striatellus, SBPH). Its function, however, remains unexplored. We investigated the molecular mechanism underlying SBPH orally secreted Vg-mediated manipulation of plant-insect interaction by RNA interference, phytohormone and H2O2 profiling, protein-protein interaction studies and herbivore bioassays. A C-terminal polypeptide of Vg (VgC) in SBPH, when secreted into rice plants, acted as a novel effector to attenuate host rice defenses, which in turn improved insect feeding performance. Silencing Vg reduced insect feeding and survival on rice. Vg-silenced SBPH nymphs consistently elicited higher H2O2 production, a well-established defense mechanism in rice, whereas expression of VgC in planta significantly hindered hydrogen peroxide (H2O2) accumulation and promoted insect performance. VgC interacted directly with the rice transcription factor OsWRKY71, a protein which is involved in induction of H2O2 accumulation and plant resistance to SBPH. These findings indicate a novel effector function of Vg: when secreted into host rice plants, this protein effectively weakened H2O2-mediated plant defense through its association with a plant immunity regulator.