Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2012
Publication Date: 3/20/2013
Citation: Shreve, J.T., Shukle, R.H., Subrqamanyam, S., Johnson, A.J., Williams, C.E., Schemerhorn, B.J., Stuart, J.J. 2013. A genome-wide survey of small interfering RNA and micro RNA pathway genes in a galling insect. Journal of Insect Physiology. 59:367-376. Interpretive Summary: Hessian fly is the most important insect pest of wheat in the southeastern United States. The most effective control of Hessian fly is through deployment of genetically resistant wheat. However, the deployment of resistant wheat places a selection pressure on Hessian fly populations that leads to the appearance of biotypes that can overcome formerly resistant wheat. One way to make wheat resistant to Hessian fly is to genetically engineer the plant so it artificially disrupts interactions necessary for the insect to survive. This approach to resistance is called “host induced gene silencing(HIGS)." However, this requires the pest has the necessary genetic pathway to facilitate disruption of critical interactions with its host plant. Recently, the Hessian fly genome was sequenced (like the sequencing of the human genome) and we have used this directory of all the genes in Hessian fly to identify genes and pathways critical to the survival of the insect. Specifically, one of the pathways we have characterized is essential for the approach to genetically engineered resistance call HIGS to work. Knowledge gained from this study will help breeders and scientists facing the challenge of devising innovative methods to ensure the durability of resistant wheat to prevent yield loss due to Hessian fly infestation. The agricultural community (crop producers and commodity groups) will benefit from improved pest control that increases yield and quality without increasing costs.
Technical Abstract: Mayetiola destructor (Say), Hessian fly, is a significant pest of wheat in most production regions worldwide. Deployment of resistance (R) genes is the most effective control for this pest; however, deployment of R genes results in an increased frequency of pest genotypes that display virulence to these R genes. RNA interference (RNAi) is a useful reverse genetics tool for studying such insect virulence pathways, but requires a systemic phenotype, which is not found in all species. In an effort to correlate our observed weak RNAi phenotype in M. destructor with a genetic basis, we have aggregated and compared RNAi related genes across M. destructor, three other insect species, and the nematode Caenorhabditis elegan. We report here the annotation of the core genes in the small interfering RNA (siRNA) and microRNA (miRNA) pathways in M. destructor. While most of the miRNA pathway genes were highly conserved across the species studied, the siRNA pathway genes showed increased relative variability. In particular, the Piwi/Argonaute/Zwille (PAZ) domain of Dicer 2 (DCR-2) had the least amount of sequence similarity of any domain between species surveyed, with a trend of increased conservation in those species with amenable systemic RNAi. Additionally, a homolog of the systemic interference defective-1 (Sid-1) gene of C. elegans was not annotated in the M. destructor genome. We hypothesize the sequence architecture of the PAZ domain in the M. destructor DCR-2 protein is related to reduced efficacy of this enzyme and this taken together with the lack of a Sid-1 homolog may account for the weak RNAi response observed to date in this species.