The ubiquitin/26S proteasome system plays a vital role in regulating host defenses against pathogens. Previous studies have highlighted different roles for the ubiquitin/26S proteasome in defense during virus infection in both mammals and plants, but their role in the vectors that transmit those viruses is still unclear. In this study, we determined that the 26S proteasome is present in the small brown planthopper (SBPH) (Laodelphgax striatellus) and has components similar to those in plants and mammals. There was an increase in the accumulation of Rice stripe virus (RSV) in the transmitting vector SBPH after disrupting the 26S proteasome, indicating that the SBPH 26S proteasome plays a role in defense against RSV infection by regulating RSV accumulation. Yeast two-hybrid analysis determined that a subunit of the 26S proteasome, named RPN3, could interact with RSV NS3. Transient overexpression of RPN3 had no effect on the RNA silencing suppressor activity of RSV NS3. However, NS3 could inhibit the ability of SBPH rpn3 to complement an rpn3 mutation in yeast. Our findings also indicate that the direct interaction between RPN3 and NS3 was responsible for inhibiting the complementation ability of RPN3. In vivo, we found an accumulation of ubiquitinated protein in SBPH tissues where the RSV titer was high, and silencing of rpn3 resulted in malfunction of the SBPH proteasome-mediated proteolysis. Consequently, viruliferous SBPH in which RPN3 was repressed transmitted the virus more effectively as a result of higher accumulation of RSV. Our results suggest that the RSV NS3 protein is able to hijack the 26S proteasome in SBPH via a direct interaction with the RPN3 subunit to attenuate the host defense response.
IMPORTANCEWe show, for the first time, that the 26S proteasome components are present in the small brown planthopper and play a role in defense against its vectored plant virus (RSV). In turn, RSV encodes a protein that subverts the SBPH 26S proteasome via direct interaction with the 26S proteasome subunit RPN3. Our results imply that the molecular arms race observed in plant hosts can be extended to the insect vector that transmits those viruses.
Rice stripe virus (RSV), one of the most destructive pathogens of rice production, has been responsible for numerous epidemics since it was first described in Japan in 1897 (1-3). RSV is the type member of the Tenuivirus genus, and the viral genome consists of four single-stranded RNA segments which range in size from approximately 8.9 to 2.1 kb (4, 5). RNA 1 is negative sense and encodes a putative RNA-dependent RNA polymerase. RNAs 2, 3, and 4 are ambisense, and each contains two open reading frames (ORFs), with one on the viral RNA strand (vRNA) and the second on the viral cRNA strand (vcRNA) (6). RSV vRNA 2 encodes a membrane-associated protein that reportedly is an RNA silencing suppressor and interacts with suppressor of gene silencing 3 (SGS3) (7). vcRNA 2 encodes a glycoprotein (NSvc2) which when expressed in insect cells is displayed on the membrane su...