RNA-MEDIATED VIRUS-RESISTANCE IN TRANSGENIC PLANTS

In recent years the concept of pathogen-derived resistance (PDR) has b een successfully exploited for conferring resistance against viruses i n many crop plants. Starting with coat protein-mediated resistance, th e range has been broadened to the use of other viral genes as a source of PDR. However, in the course of the efforts, often no clear correla tion could be made between expression levels of the transgenes and obs erved virus resistance levels. Several reports mentioned high resistan ce levels using genes incapable of producing protein, but in these cas es, even plants accumulating high amounts of transgene RNA were not mo st resistant. To accommodate these unexplained observations, a resista nce mechanism involving specific breakdown of viral RNAs has been prop osed. Recent progress towards understanding the RNA-mediated resistanc e mechanism and similarities with the co-suppression phenomenon will b e discussed.