A virus plays a role in partially suppressing plant defenses induced by the viruliferous vectors.

Herbivorous attack induces plant defenses. There is evidence that some pests suppress these defenses by interfering with signaling pathways. We here report that infestation by the white-backed planthopper, Sogatella furcifera, induces defense responses in rice and infection of the southern rice black-streaked dwarf virus in the planthoppers partially suppresses the planthopper-induced plant defenses. Salicylic acid (SA) levels generally showed a temporal increase pattern while jasmonic acid (JA) levels generally exhibited a decrease pattern in the planthopper-infested plants, irrespective of virus infection status in the insects. The increase in SA was less while the decrease in JA was more in the viruliferous insect-infested plants than in the nonviruliferous insect-infested plants at both 48 and 72 h post infestation. The phytohormone levels corresponded to the patterns of relative expression levels of SA-marker genes (ICS1 and NPR1) and JA-marker gene (AOS2) in the plant treatments. Planthoppers performed better on the uninfested plants than on the previously infested plants and were of not significant increase in performance on the plants previously attacked by viruliferous planthoppers in comparison with the plants previously attacked by nonviruliferous insects. Our results indicate that the virus plays a role in partially suppressing the plant defenses induced by the planthopper. These findings provide a new perspective on plant-virus-vector interactions.