Functional analyses of dopamine receptors involved in virus transmission and reproduction in the small brown planthopper Laodelphax striatellus

Dopamine (DA) is the most abundant biogenic amine present in the insect central nervous system, and regulates multiple functions in physiology and behaviors through dopamine receptors (DARs). The small brown planthopper Laodelphax striatellus is an important agricultural pest and causes serious damage by transmitting diverse plant viruses, such as rice stripe virus (RSV). However, DARs have not yet been molecularly characterized in planthoppers, and their roles in virus infection and transmission remain largely unknown in insect vectors. In this study, we cloned four LsDARs (LsDOP1, LsDOP2, LsDOP3 and LsDopEcR) from L.striatellus. LsDARs share considerable sequence identity with their orthologous DARs, and cluster nicely with their corresponding receptor groups. The transcript levels of LsDARs varied in different developmental stages and adult tissues, with the highest expressions in the egg stage and in the brain. The expression levels of LsDARs were significantly higher in RSV-viruliferous L.striatellus. Knockdown of LsDOP2 and LsDOP3 significantly downregulated the expressions of viral genes of capsid protein (CP) and RNA3 segment (RNA3), while LsDOP1 knockdown upregulated their expressions. Silencing LsDopEcR upregulated and then downregulated CP and RNA3 expressions. Moreover, LsDOP2 and LsDOP3 knockdown significantly decreased the vertical transmission rates of RSV. Meanwhile, DA injection promoted RSV transmission and accumulation. We further demonstrated that silencing of LsDARs significantly altered the expressions of vitellogenin (LsVg) and Vg receptor (LsVgR). Furthermore, the reproduction performance of L.striatellus was reduced by LsDOP2 and LsDOP3 knockdown, but increased by LsDopEcR knockdown, and not affected by LsDOP1 silencing. These results provide critical information concerning the roles of DARs in virus transmission and reproduction in L.striatellus, and open the way for the development of innovative strategies for planthopper control.