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USDA Kicks off Four Research Programs Involving RNAi Gene Silencing

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NEW YORK (GenomeWeb) – The US Department of Agriculture launched four research programs last month with an RNAi component, including ones related to the effect of climate change on disease-carrying insects, and pest-resistance and fungal contamination in plants.

In addition, earlier this month agency researchers began an effort to develop RNAi-based methods to control mosquitoes and other biting arthropods.

The first project centers around the effects of climate change on insects that act as vectors for diseases. Environmental temperature is known to affect the development of such insects, as well as their ability to acquire, maintain, and transmit a pathogen. Yet, according to the USDA, the relationship between temperature and vector competence is poorly understood.

And while the insect immune system is "a likely player at the intersection of temperature, insect physiology, and vectorial capacity … surprisingly few studies have explored the consequences of temperature fluctuations and seasonality on the immune system of important insect vector species," the agency said in a project abstract.

A recent study by scientists at Virginia Tech University investigated the effects of temperature on the RNAi-based antiviral pathways of mosquitoes. They found that insects that matured at lower temperatures had a deficiency in RNAi, which was associated with higher levels of infection with chikungunya and yellow fever viruses.

In light of such work, USDA researchers Scott McVey and colleagues have begun investigating if this temperature-associated infection susceptibility occurs in other insects that act as vectors of disease including Culicoides sonorensis, a type of biting midge.

The USDA team aims to use a gene-silencing approach to suppress different branches of the Culicoides immune system, including RNAi and actin remodeling, and "assess their impact on viral infection and dissemination," according to the agency. In parallel, the investigators will determine if larval rearing temperature influences viral infectivity of adult midges.

The second program focuses on Pratylenchus penetrans, a pest also known as the root lesion nematode (RLN) that extracts nutrients from the roots of plants including wheat, chickpea, and soybean.

In an effort to develop transgenic plants — specifically lilies — resistant to RLNs, USDA scientist Kathy Kamo is working to uncover the molecular mechanisms by which the insect interacts with host plants and identify essential metabolic and parasitism genes that can be used for its control.

She and her colleagues then aim to investigate whether RNAi can be used to induce host resistance to RLNs by silencing the candidate genes identified in the project, as well as known RNAi lethal phenotypes in another nematode, Caenorhabditis elegans.

Also looking to use RNAi for plant protection is USDA scientist Jeffrey Cary, who hopes the gene-silencing technology can control pre-harvest corn contamination with aflatoxin, a myotoxin produced by the fungi Aspergillus flavus and Aspergillus parasiticus that poses a threat to both humans and livestock.

Cary plans to use information obtained from A. flavus proteomic and genomic studies to identify candidate fungal genes that are required for successful invasion and aflatoxin production during corn interaction, according to the USDA. Vectors expressing shRNAs targeting these genes will be created and tested against the fungus.

The most promising shRNA vectors will be optimized for expression in corn and introduced into the plant, and the seeds from these transgenic plants will be tested for the presence of the RNAi molecules.

Finally, seeds from positive lines will be used in kernel screening assays to determine if expression of target fungal genes is significantly downregulated and leads to decreased fungal growth and aflatoxin production.

The final USDA project, headed by Ulrich Bernier, seeks to discover and develop new repellants and toxicants for mosquitoes and similar insects, including insecticides based on gene-silencing dsRNAs.

Such RNAi molecules, the agency stated, could serve as a novel and safe means of controlling biting insects.

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