CSIRO looks at RNAi for plants and pest control

An ambitious project to knock-out the 25,000-plus genes of Arabidopsis one at a time using RNA interference (RNAi) is being developed by a European consortium headed by Ian Small at France's Unit‚ de Recherche en Genomique Vegetale (URGV) using a plasmid vector designed by CSIRO Plant Industry researchers to deliver hairpin RNA constructs.

The vector, dubbed pHELLSGATE, will be used to deliver the RNAi to the plant via Agrobacterium transfection. According to CSIRO's Peter Waterhouse, the eventual objective of the AGRIKOLA (Arabidopsis Genomic RNAi Knock-out Line Analysis) project is to create a large collection of knockout Arabidopsis strains for further study plus a library of plasmids or bacteria that can be used to create more knockouts.

Waterhouse, who presented data on RNAi in plants at the Lorne Genome Conference recently, said that RNAi was a powerful technique suitable for looking at gene function in plants, and the vector was specifically designed to be used in genome-wide surveys like AGRIKOLA.

Plants have developed their own RNAi-based defence mechanisms to protect against virus infection, he said, in addition to the use of micro RNAs as regulators of gene expression.

RNAi-based pest control

In addition to its role as a tool to explore the mysteries of the genome, CSIRO researchers are also exploiting RNAi as a possible mechanism for controlling pest animals. Steven Whyard from CSIRO Entomology presented a number of possible applications at the Lorne Genome Conference.

In one project aimed at finding new targets for chemical insecticides, the researchers are knocking out Drosophila genes with tetracycline-repressible RNAi allowing the RNAi to be timed to particular developmental stages. Already the project has netted 41 phenotypically significant genes out of 52 looked at so far, Whyard said.

But the use of RNAi is not restricted to finding target genes for pesticide development.

"One of the things we are interested in doing is turning RNAi into a species-specific pesticide," said Whyard. This could potentially be accomplished, he said, by finding species-specific sequences in the variable regions of genes. The RNAi constructs would not affect non-target organisms, and Whyard believes regulatory authorities might find the idea appealing.

A related project, which Whyard is working on with CSIRO Marine Research, and CSIRO Sustainable Ecosystems, is the development of 'sterile ferals' -- organisms with repressible fertility that could be used to control populations of pest animals as diverse as Pacific oysters and fruit flies.

In this application, developmentally important genes such as the Hox genes are repressibly silenced to give a functional sterility. In containment, the organism can breed when given the repressor, but in the wild where the repressor is not present, sterility results. Similarly, silencing sex-determination genes creates male-only populations, an approach exploited by CSIRO's 'daughterless' carp project.

While the application has its limitations, not least in the ability of the RNAi to completely silence genes, Whyard believes that the sterile feral approach is worth considering as a method to develop GMOs for pest control.