Viral interference with gene silencing in non-transgenic or transgenic plants

Various agronomically interesting traits have been obtained by inducing post-transcriptional gene silencing (PTGS) in transgenic cultivated crops. Some plant cultivars that were created by interspecific crosses also display PTGS-induced phenotypes. The finding that many plant viruses have the ability to counteract PTGS raises the possibility that viral infection may cause the loss of PTGS-induced traits in transgenic as well as non-transgenic plants. We addressed this question by studying virus-specific differences in the interference with silencing of the chs-A gene in non-transgenic RedStar-type petunia whose flowers display variegated flowers resulting from natural PTGS of the chs-A gene. Our results show that potato potyvirus Y (PVY), tobacco etch potyvirus (TEV) and cucumber mosaic cucumovirus (CMV), which are known to inhibit PTGS, induce specific phenotypic changes resulting from spatially-regulated interference between viral infection and PTGS of the chs-A gene. However, PTGS breakdown was not total, and the pattern observed depended on which virus was involved. This suggests that the degree of interference with PTGS will depend on the pattern of expression of the silenced gene and on that of the accumulation of the potentially interfering virus. We are currently studying the effects of viral infection by TEV or CMV on PTGS-induced resistance to PVY in transgenic tobacco lines expressing a PVY coat protein gene. Preliminary results suggest that the two viruses have different effects. These results show that viral infections could lead to the loss of agronomically interesting traits obtained by PTGS in either transgenic or non-transgenic plants, such as flower color, virus-resistance, or modified seed oil composition. (Résumé d'auteur