Pathogen Derived Resistance and Reducing the Potential to Select Viruses with Increased Virulence

Pathogen derived resistance (PDR) refers to using sequences from a pathogen to protect the host from the effects of the pathogen (Sanford and Johnson, 1985). Following the first example of coat protein (CP)-mediated resistance, a type of PDR, to protect transgenic tobacco plants from infection by tobacco mosaic virus (TMV) (Powell-Abel et al., 1986) there have been many reports of different types of PDR. Genes that produce virus-derived antisense RNAs, (+) sense RNAs that do not encode proteins, modified and wild type replicases, and wild type and mutant cell-cell movement proteins have been used to confer resistance. Certain gene strategies appear to be more effective than others depending upon the virus and host. Likewise, certain strategies are anticipated to be more useful in agricultural settings than others. To date, the most common type of PDR in advanced stages of development is CP-mediated resistance; furthermore, government regulatory agencies have approved the use of CP genes to protect plants in agriculture. Other types of genes are being reviewed for similar status. During the technical stage of development and applications of PDR, a variety of questions have been raised related to the relative safety of transgenic plants that contain virus-derived gene sequences. Some of the concerns are based upon lack of understanding of the methods used to develop resistance, or the biology of virus infection and disease, while certain concerns have some degree of validity. This short paper highlights several of the arguments offered to restrict the use of PDR and those presented to promote its use. This is followed by a summary of recent results that show that knowledge of mechanisms of resistance can lead to increased efficacy of PDR and can reduce concerns about safety and durability of PDR in agriculture. Pathogen Derived Resistance and Reducing the Potential to Select Viruses with Increased Virulence