Strategies and mechanisms of plant virus resistance

Virus-induced diseases are responsible for major crop losses worldwide. A better understanding of plant defense mechanisms would lead to the development of novel strategies for effective plant protection. Early protein-based approaches relied mostly on the expression of transgenic coat protein (CP) to block the progression of the virus infectious process. Other strategies exploit the plant's innate defense mechanisms to combat invading viral pathogens. For example, the RNA-based resistance makes use of the plant post-transcriptional gene silencing (PTGS) mechanism to degrade viral RNAs. In cross-protection the prior inoculation with a mild viral strain confers resistance against a severe strain. Although the molecular detail of cross-protection is not fully understood, it is likely to be comprised of both protein-and RNA- based mechanisms, as well as some other unknown processes. In this review article we compare the benefits and challenges of these different viral-resistance approaches. Furthermore, we discuss the development of a new approach based on the plant's miRNA pathway. Artificial miRNAs with sequences complementary to viral sequences have been successfully used to generate virus resistance. This novel anti-viral strategy, which has the advantage of reducing possible bio-safety risks associated with protein-and RNA based strategies, is a first step toward designing environmentally friendly virus resistance in transgenic crops.