Abstract
The Asian rice gall midge, Orseolia oryzae (Wood-Mason), is a serious pest of rice. Investigations into the gall midge-rice interaction will unveil the underlying molecular mechanisms which, in turn, can be used as a tool to assist in developing suitable integrated pest management strategies. The insect gut is known to be involved in various physiological and biological processes including digestion, detoxification and interaction with the host. We have cloned and identified two genes, OoprotI and OoprotII, homologous to serine proteases with the conserved His87, Asp136 and Ser241 residues. OoProtI shared 52.26% identity with mosquito-type trypsin from Hessian fly whereas OoProtII showed 52.49% identity to complement component activated C1s from the Hessian fly. Quantitative real time PCR analysis revealed that both the genes were significantly upregulated in larvae feeding on resistant cultivar than in those feeding on susceptible cultivar. These results provide an opportunity to understand the gut physiology of the insect under compatible or incompatible interactions with the host. Phylogenetic analysis grouped these genes in the clade containing proteases of phytophagous insects away from hematophagous insects.
Highlights
The Asian rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera: Cecidomyiidae), is the third most destructive insect pest of rice (Oryza sativa L.) with an average annual yield loss worth US $80 million in India alone [1]
Owing to extensive cultivation of resistant cultivars the insect has been evolving into new biotypes [3] that are able to overcome the host resistance
When feeding on resistant cultivars, larvae are killed within 24–96 h. This could be brought about by the inability of the larvae to digest and/or detoxify the ingested plant material. We thought it pertinent to investigate the significance of gut proteases having a role in this interaction as suggested in the case of the Hessian fly, a midge of wheat and another member of the family
Summary
The Asian rice gall midge, Orseolia oryzae (Wood-Mason) (Diptera: Cecidomyiidae), is the third most destructive insect pest of rice (Oryza sativa L.) with an average annual yield loss worth US $80 million in India alone [1]. Maintain normal levels of gut proteolysis [17] Owing to these observations, coupled with the fact that serine proteinases are the most abundant gut proteins in feeding larvae, it is hypothesized to play an important role in the interaction of the gall midge with its rice host. We have investigated expression of the genes encoding digestive serine protease-like enzymes in the rice gall midge feeding on susceptible and resistant cultivars. As far as we know this is the first report of the cloning of genes that encode proteases in the rice gall midge and their differential expression in compatible and incompatible interactions. We believe that this study will be a step towards providing a better understanding of the interaction between rice gall midge and its host that would eventually ensure development of better strategies for protecting rice from this economically important pest
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