Virus resistance in plants-the unconventional approach

The combination of successful transformation strategies with molecular genetics methodologies has made it possible to use novel approaches to create virus resistance in plants. The concept for nonconventional protection proposed by Sanford and Johnston (81) based on the understanding of the mechanisms of host-pathogen interaction has provided the ground to engineer pathogen resistance. The principle is to interfere with and disrupt the pathogenic process by expressing in the host, pathogen genes coding for molecules essential for the pathogen. The possibility that viral genes could function as resistance genes in plants has been demonstrated on a rapidly growing number of plants and for different groups of plant viruses. Examples of pathogen derived resistance in plants have been reported using various approaches: ex:pression of viral capsid genes, antisense sequences, complete viral genome, satellite RNAs, defective interfering molecules, nonstructural gene sequences and ribozymes.