Plant-Virus Interactions

 

A major area of investigation in the Sacco lab is the interactions between the polerovirus species Turnip yellows virus and Potato leafroll virus with plants in the Nicotiana genus (tobaccos). We are particularly interest in the protein P0, an important determinant of virulence for the poleroviruses in their host plants. P0 is a viral suppressor of RNA silencing. RNA silencing is a plant defense mechanism that recognizes foreign viral RNAs and targets them for degradation. P0 interferes with this mechanism by causing the elimination of a key component, proteins called the Argonautes (AGOs).

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Expression of P0 in Nicotiana leaves can be used to study its function as a VSR or in induction of a type of programmed cell death called the hypersensitive response (HR). For VSR function, we express P0 with a green fluorescent protein (GFP) and look for green fluorescence under UV light (the plant's green chlorophyll appears red under UV light). If the GFP gene is expressed alone, there will be no fluorescence seen under UV light 6 days after the leaves were infiltrated (bottom patch on the right side). If P0 induces HR, the patch will appear dead (top patch on the right side). We have created mutants of P0 that disrupt its ability to elicit HR, but preserve its RNA silencing suppression activity, seen by green fluorescence in the rest of the patches.

 

Our current research is aiming to study the protein-protein interactions between P0 and proteins of the host cell to fully understand how P0 causes HR or suppresses RNA silencing in different plants. We are using molecular biology and biochemical approaches to define important regions of P0 for function, to identify proteins with which it interacts and to identify genes in Nicotiana glutinosa that are differentially regulated in defense signaling that leads to HR versus extreme resistance.
 

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Animal Endogenous Retroviruses (ERVs)

 

All eukaryotic genomes have endogenous retroviruses (ERVs) that are DNA copies of ancient retroviruses that integrated into a host germ-line cell and became a permanent part of the host's DNA. ERVs are transmitted to offspring, so inherited in a Mendelian fashion.

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We previously studied the chicken (Gallus gallus) genome for ERV elements that have intact genes that could contribute to retroviral particle production, recently characterizing one element: GGERV20. Since chicken cells are used to grow virus for human vaccination, it is important to understand all potential virus components in these vaccine substrates. GGERV20 has many copies present in the chicken genome, which we showed are still segregating in the population and have not become fixed, but it lacks an envelope glycoprotein gene and can contribute only the internal core proteins of a virion.

 

Current studies are investigating ERVs from nematodes. We are interested in the plant-parasitic nematodes that infect the roots of crops and cause losses to agriculture. Recent advances in genome sequencing has allowed us to leverage public databases to identify a unique ERV from nematodes. This nematode ERV (NERV) appears to have evolved from a retrotransposon-like element that stole an envelope glycoprotein gene from another RNA virus and moved widely throughout the phylum Nematoda.