Transgenic accumulation of a defective cucumber mosaic virus (CMV) replicase derived double stranded RNA modulates plant defence against CMV strains O and Y in potato.

Cucumber mosaic virus is an important plant pathogen with a broad host range encompassing many plant species. This study demonstrates the production of transgenic potato lines exhibiting complete resistance to cucumber mosaic virus strain O and Y by post transcriptional gene silencing. Two constructs were used, one, pEKH2IN2CMVai, contains inverted repeat of 1,138 bp fragment of a defective CMV replicase gene derived from RNA2 of cucumber mosaic virus strain O (CMV-O), while the other, TRV-based VIGS vector (pTRV2CMVai), contains the same fragment of the replicase gene, but without inverted repeat. These constructs were used to produce transgenic potato lines of cultivar 'Danshaku', a susceptible genotype to CMV. Transgenic lines derived from pEKH2IN2CMVai accumulated small interfering RNA (siRNA) before and after virus challenge, whereas those derived from pTRV2CMVai showed siRNA expression after virus challenge. When transgenic lines were challenged with CMV-O or CMV-Y, four lines exhibited complete (100%) resistance to both strains, whereas the other lines had high levels of resistance. Infectivity of CMV-O was lower than that of CMV-Y in the highly resistant plants. There were no significant differences with regard to resistance between plants derived from pEKH2IN2CMVai and those obtained from pTRV2CMVai. The presence of CMV-specific siRNA in the resistant phenotypes indicates that the resistance was acquired through RNA silencing.