Team:SSHS-Shenzhen/Description
Background
Pests have caused billions of dollars in agricultural losses. Phyllotreta striolata is one of the most serious pests of vegetable crops worldwide. At present, the major approach to control P. striolata is to use chemical pesticides, which have resulted in dietary pesticide pollution and environmental destruction, thus caused significant hazards to human health and the environment. The alternative commercial biotechnological approach to controlling insect pests relies mainly on the expression of Bacillus thuringiensis (Bt) insecticidal proteins, but Phyllotreta striolata is resistant to biopesticide Bacillus thuringiensis (Bt). Therefore, there is a critical need to develop economically, and ecologically, methods to control this this highly destructive agricultural pest. In recent years, RNAi has been used to downregulate the expression of specific genes, RNAi based transgenic plants producing dsRNAs directed against insect genes in Lepidoptera and Coleoptera pest species have been reported. In our project, we use topically application of siRNA/shRNA to control P. striolata
What is the mechanism of RNAi-based approach?
RNA interference (RNAi) is a biological process that inhibits the expression of target genes. Eukaryotic organisms including insects, possess this RNAi mechanism for sequence specific gene silencing that is triggered by the introduction of double-stranded RNA (dsRNA). A long dsRNA can be either artificially or naturally introduced into the cell. Once inside the cell, the dsRNA is cleaved into ~21 bp small interfering RNA (siRNA) by an enzyme called Dicer (Bernstein et al., 2001; Hamilton & Baulcombe, 1999, Science 286: 950), thus producing multiple “trigger” molecules (siRNA) from the original single dsRNA. One strand of each siRNA is loaded into Agoraute, an endonuclease, to form an RNA-induced Silencing Complex (RISC), thus guiding the RISC to the target mRNA resulting in the effective cleavage and subsequent degradation of the target mRNA. The mechanism of RNAi is illustrated in Fig. 1.
Degradation of the mRNA leads to the silence of its gene. When the important gene of the insect is silenced, the insect will be killed.
Fig. 1 siRNA silencing crucial genes
Why do we use topical application approach instead of transgenic approach?
Because transgenic approach may raise concerns about environment and food safety, and topical application of effector molecules (such as dsRNA or siRNA) can also trigger the RNAi mechanism, this approach is convenient to operate and does not involve transgenic plants, thus is easier to be accepted by people.
References
Zhao, Y.Y., Yang, G., Pruski, W. and You, M.S. (2008) Phyllotreta striolata (Coleoptera: Chrysomelidae): arginine kinase cloning and RNAi-based pest control. Eur J Entomol 105: 815–822.
GORDON K.H. & WATERHOUSE P.M. 2007: RNAi for insect-proof plants. Nat. Biotech.25: 1231–1232.
BAUM J.A., BOGAERT T., CLINTON W., HECK G.R., FELDMANN P., ILAGAN O., JOHNSON S., PLAETINCK G., MUNYIKWA T., PLEAU M., VAUGHN T. & ROBERTS J. 2007: Control of coleopteran insect pests through RNA interference. Nat. Biotech. 25: 1322–1326.
MAO Y.B., CAI W.J., WANG J.W., HONG G.J., TAO X.Y., WANG L.J., HUANG Y.P. & CHEN X.Y. 2007: Silencing a cotton bollworm P450 monooxygenase gene by plant-mediated RNAi impairs larval tolerance of gossypol. Nat. Biotech. 25: 1307–1313.
TURNER C.T., DAVY M.W., MACDIARMID R.M., PLUMMER K.M., BIRCH N.P. & NEWCOMB R.D. 2006: RNA interference in the light brown apple moth, Epiphyas postvittana (Walker) induced by double-stranded RNA feeding. Insect Mol. Biol. 15: 383–391.
YIYING ZHAO, GUANG YANG1, GEFU WANG-PRUSKI and MINSHENG YOU. Phyllotreta striolata (Coleoptera: Chrysomelidae): Arginine kinase cloning and RNAi-based pest control. Eur. J. Entomol. 105: 815–822, 2008
Macrae IJ, Zhou K, Li F, Repic A, Brooks AN, Cande WZ, Adams PD, Doudna JA (January 2006). "Structural basis for double-stranded RNA processing by Dicer". Science. 311 (5758): 195–8..