Rice stripe virus (RSV) is one of the serious plant pathogenic viruses for rice transmitted by small brown planthopper, SBPH, Laodalphax striatellus. RNA interference (RNAi) is an universal gene-knockdown mechanism in eukaryotic organisms which includes insects，and has been considered as an alternative strategy to control insect pests. Hence, we applied this technique to interfere the translation of target RNA genes to knockdown the virus gene on RSV-viruliferous L. striatellus. Three out of seven RSV genes, RdRp, NS3, and NCP were used as target genes and each dsRNA targeting the viral genes were delivered to the insects indirectly through the rice leaves by irrigation. As a result, not only the relative expression level of target genes decreased but also those of non-target genes and the replication of RSV genome as well. In summary, leaf-mediated dsRNA feeding methods would be useful in the knockdown of target genes on piercing-sucking insects. The genes used in this experiment can be utilized for the development of pest-resistant transgenic plants based on RNAi.

Rice stripe virus (RSV) is one of the serious plant pathogenic viruses for rice and mediated by small brown planthopper, Laodalphax striatellus. So far, the studies have been mainly focused on the interaction between the host plant and the virus. In this study, for better comprehension of the interactions among Rice stripe virus, rice and small brown planthopper, transcriptomes of the RSV-viruliferous (RVLS) and non-viruliferous L. striatellus (NVLS) were comparatively analysed. For this, non-viruliferous L. striatellus were collected from non-infected rice field and fed RSV-infected rice for 5 days. With the RNAs prepared from the RSV-viruliferous and the non-viruliferous small brown planthoppers, we conducted Illumina RNA sequencing (Hiseq 2000) and then two transcriptome databases were generated from RVLS and NVLS, respectively. The transcriptome of RVLS and NVLS were campared to figure out how the gene expression of the insects affected by Rice Stripe Virus. RSV-dependently regulated genes analysed from this study may have important functions in the transmission and replication of RSV.

Melanization is a unique defence mechanism in arthropods involved in wound healing and pathogen encapsulation. Phenoloxidases (PPOs) are key enzymes of melanization, which mediate the enzymatic conversion of tyrosine to eumelanin. A serine-protease (SP) cascade, similar to the blood-clotting cascade of vertebrates, proteolytically activates prophenoloxidases to phenoloxidases. This proteolytic activation is tightly controlled by serpins and other melanization inhibitors. Melanization has been regarded as one of key immune responses against malaria parasites in mosquitoes. The ookinete melanization of both the simian malaria parasite, Plasmodium cynomolgi, and of the rodent parasite, Plasmodium berghei, prevent parasite development in the human malaria vector, An, gambiae. However, the recent studies revealed a melanization response regulated by Serpin-2 and two C-type lectins (CTL4 and CTLMA-2) was shown to result in ookinete melanization but did not affect the development of the natural human parasite P. falciparum in the mosquito. Instead of melanization, TEP1/APL1/LRIM1 complement-like pathway has been identified as major immune response that regulate parasite loads in the natural association of An. gambiae and P. falciparum. The studies by me and my colleagues revealed another melanization response independent on Serpin-2. Genome analyses of mosquitoes revealed a large expansion of the PPO, SP, and serpin genes potentially involved in the melanization pathway. This expansion was devoted to existence of at least two distinct SP-Serpin regulation modules in controlling separate melanization responses, tissue and hemolymph melanization, in the mosquito, Aedes aegypti. Tissue melanization regulated by Serpin-2 has role in melanotic tumor formation, but not in ookinete melanization. Hemolymph melanization regulated by Serpin-1 and a couple of SPs was activated by the infection of various pathogens and is involved in anti-malarial defense against the avian malaria parasite, P. gallinaceum. A new type of regulator, CLSP2, negatively modulate this hemolymph melanization. Cross-talk between hemolymph melanization and complement-like pathway will be discussed.