Abstract
Many economically important crops are attacked by a number of species of the genus Potyvirus. Appropriate transgenic plants conferring multiple resistance against potyviruses may help reduce the agricultural loses significantly. In this investigation, transgenic Nicotiana benthamiana plants carrying the conserved regions of potyviral HC-Pro, CIP, NIb and CP genes, engineered from Turnip mosaic virus (TuMV), were generated for control of potyviruses by post-transcriptional gene silencing (PTGS) mechanism. To compare the effectiveness of different combinations of the conserved regions for confering resistance against potyviruses, different transgenic lines carrying single, double, triple and tetra combinations of the conserved regions were generated by Agrobaterium-mediated transformation. In a similar proportion, transgenic tobacco lines carrying each construct were able to provide complete resistance of immunity to TuMV infection. To assess the broad-spectrum resistance of the transgenic lines, all TuMV-immune lines were further challenged with four other potyviruses, i.e., Bean common mosaic virus (BCMV), Sweet potato latent virus (SPLV), Yam mosaic virus (YMV) and Passionfruit woodiness virus (PWV), which have different phylogenetic distances from the homologous TuMV. The results showed that TuMV-immune tHC5-16, tNIb7-11, tHC20-13+CIP, tHC+CIP+NIb30-12 and tHC+CIP+NIb+CP32-5 transgenic tobacco lines conferred different levels of resistance in delaying symptom expression (4 - 25) after separate inoculation with YMV, BCMV and PWV. Northern hybridization analysis revealed that the levels of accumulation of siRNA were positively correlated to the levels of resistance of transgenic lines. It is inferred that the multiple combination of the conserved regions has a better effect for resistance durability, since the chances for mutations at multiple genes to overcome PTGS by a potyvirus are much less than mutations at a single gene. Among the four individual single constructs, we conclude that the transgenic lines carrying the conserved regions of HC-Pro or NIb gene have higher capability for conferring broad-spectrum resistance against potyviruses.
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