Introduction

Engineered resistance (or genetically engineered resistance) to viral pathogens refers to the introduction and expression of foreign genes, termed transgenes, in plants such that expression of a transgene interferes with the virus life cycle and thereby confers resistance to the virus. Advances in plant transformation technologies for a variety of plant species have resulted in the introduction of transgenes from a variety of sources that confer resistance to viral pathogens. The transgenes are stably integrated into the plant genomes, are heritable, and resistance segregates with the transgenes. In many cases, transgenic plants have been generated that have resistance to viruses by mechanisms that do not occur naturally and could not have been introduced into the plants by traditional breeding techniques. Genetically engineered virus resistance in crop plants shows great promise in efficiently reducing losses due to virus disease and complements traditional plant breeding.

Transgenes are designed as chimeric genes under the control of a promoter and contain nonviral sequences at the 3' end to provide transcription termination and polyadenylation signaling. With few exceptions the preferred promoter has been the 35S promoter from the plant DNA virus cauliflower mosaic virus, which is constitutively expressed and drives high levels of expression of transgenes in most plant tissues. In some cases, the transgene is placed under the control of a tissue-specific promoter to localize expression of the transgene.

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