Reduction of potato mop-top virus accumulation and incidence in tubers of potato transformed with a modified triple gene block gene of PMTV

Potato mop-top virus (PMTV) RNA 2 contains a triple gene block (TGB) that consists of a set of three overlapping genes. These genes encode three proteins necessary for viral cell-to-cell movement. The gene encoding for the second triple gene block protein, TGB2, was mutated in a region that is highly conserved among TGB2 proteins from different viruses. The mutated TGB2 gene, under transcriptional control of the 35S promoter from cauliflower mosaic virus, was transformed into potato (Solanum tuberosum cv. Hulda) by Agrobacterium-mediated transformation. Ten of the transgenic lines obtained, all of which were shown to transcribe the introduced gene, were evaluated for resistance to PMTV in a field trial. Tubers from the field were analysed for virus content by ELISA. In seven of the transgenic lines analysed there was a reduction in ELISA values relative to a non-transgenic control line. In the three lines that had the lowest ELISA readings this reduction was manifested both as a reduction in the proportion of infected tubers and as a reduction in virus levels in infected tubers. In the line showing the highest level of resistance, the total ELISA value was reduced by 79%. These results demonstrate that the introduction of a mutated TGB2 gene into potato can confer increased resistance to PMTV.