Natural and Engineered Defenses Against Plant Viruses

Background: Plants live in a dynamic environment subjected to frequent pathogenic and environmental stresses and have evolved diverse self-defense pathways for their survival. Many of these defense responses are energy-intensive and antagonistic against each other to enable prioritization of strong targeted responses. Viruses cause significant damage in the agricultural and natural world. They are obligate intracellular pathogens that depend on their host cell for replication and movement. Method: We searched bibliographic databases for peer-reviewed research literature on the topic of natural and engineered plant defense responses against plant viruses. Results: While programmed cell death is an appropriate initial defense response to isolate viruses, RNA silencing or the RNAi pathway presents a highly effective defense mechanism that plants employ against virus attack. But RNA silencing is also essential for normal gene regulation within the host. RNA silencing largely dominates the literature on plant virus defense, but there are a number of other effective defense mechanisms that will be discussed. Conclusion: This review first covers different viral replication strategies based on genome organization, then presents an overview of known virus defense mechanisms and pathways, and finally highlights recent work and new strategies to engineer viral resistance in crop plants.