Tolerance and responsive gene expression of Sogatella furcifera under extreme temperature stresses are altered by its vectored plant virus

Southern rice black-streaked dwarf virus (SRBSDV), a newly emerged fijivirus causing great loss to rice production in eastern and southeastern Asian countries in recent years, is efficiently transmitted by a rice pest, white-backed planthopper (WBPH, Sogatella furcifera) in a persistent, circulative propagative manner and can be considered as an insect virus. In this study, SRBSDV infection in WBPH was found to increase the vector's death rate under extreme cold stress but improve its survival rate under extreme heat stress. Digital gene expression profiling based on RNA-Seq revealed different gene regulation patterns in WBPH under viral and/or temperature stress. Under cold stress, the virus infection upregulated 1540 genes and downregulated 131 genes in the insect, most of which were related to membrane properties and biological processes of actin and cytoskeleton; whereas under heat stress, it upregulated 363 genes and downregulated 548 genes, most of which were associated to metabolism and intracellular organelles. Several types of stress-responsive genes involving intestinal mucin, cuticle protein, ubiquitin protease, immune response, RNA interference and heat shock response, were largely upregulated under cold stress, but largely downregulated under heat stress, by SRBSDV infection. Our results suggest two distinct mechanisms of virus-altered vector insect tolerance to temperature stress.