Tetraspanin SfCD9 as a Key Membrane Binding Factor of SRBSDV P10 Facilitates Viral Entry Into Sogatella furcifera Midgut Epithelial Cells via Clathrin-Mediated Endocytosis.

Southern rice black-streaked dwarf virus (SRBSDV), transmitted by Sogatella furcifera, causes significant rice yield losses in Asia. So far, the mechanism by which SRBSDV traverses the midgut barrier to establish infection in S. furcifera midgut epithelial cells remains unknown. Here, we show that SRBSDV P10, the major outer capsid protein, enters S. furcifera midgut epithelial and haemolymph cells through interacting with the tetraspanin SfCD9 highly expressed in midgut and haemolymph cells. SfCD9 co-localises with SRBSDV P10 and relocates it from the endoplasmic reticulum (ER) to the cytomembrane of co-expressing Sf9 cells. SfCD9 localises on the cell membrane and in the cytoplasm in nonviruliferous S. furcifera midgut epithelial cells. SRBSDV P10 and SfCD9 colocalised on the midgut epithelial cell membrane of viruliferous S. furcifera at 2 days post-virus feeding (dpvf), and predominantly colocalised in epithelial cell cytoplasm at 6 dpvf. Knockdown of SfCD9 or oral delivery of the anti-SfCD9 antibody significantly inhibited SRBSDV invasion in S. furcifera. SRBSDV from infected rice crude extracts can enter SfCD9-expressing Sf9 cells, but not wild-type Sf9 cells. SfCD9 serves as a key membrane binding factor for SRBSDV entry into vector midgut epithelial cells via clathrin-mediated endocytosis. Collectively, these findings offer valuable insights into SRBSDV transmission and identify SfCD9 as a potential target to disrupt viral transmission.