Fig. 8: Proposed model of RGDV-mediated the inhibition of CBP expression to promote viral transmission by leafhopper vectors.

CBP can compete with Pns11 of RGDV to bind to cytoplasmic actin, the main component of the apical plasmalemma. Before viral infection of salivary glands, CBP directly attaches to the actin-based apical plasmalemma and then is secreted as a major salivary component. However, viral infection significantly inhibits CBP expression, and thus virus-loaded Pns11 filaments can attach to actin-based apical plasmalemma and induce an exocytosis-like process for viral secretion into salivary cavities. The reduction of CBP secretion increases cytosolic Ca²⁺ levels in rice plants, triggering substantial callose deposition and H₂O₂ production. Thus, viruliferous vectors encounter stronger feeding barriers and would probe more frequently and secrete more saliva into rice plants, ultimately enhancing viral horizontal transmission. APL apical plasmalemma, SC secretory cytoplasm, Cv cavity, SD salivary duct.