Transgenic expression of the Agrobacterium tumefaciens single-stranded DNA binding protein VirE2 provides resistance to both bipartite and monopartite betasatellite-associated begomoviruses in Nicotiana benthamiana

Viruses of the genus Begomovirus (family Geminiviridae) are a threat to agriculture and food security throughout the warmer parts of the world. Begomoviruses are transmitted by the whitefly Bemisia tabaci and have genomes consisting of one (monopartite) or two (bipartite) circular, single-stranded (ss) DNA molecules. Most monopartite begomoviruses also associate with host range and symptom exacerbating satellites known as betasatellites. Cotton leaf curl Kokhran virus (CLCuKoV), in association with the betasatellite cotton leaf curl Multan betasatellite (CLCuMuB), is one of a number of viruses that cause cotton leaf curl disease in southern Asia. Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus widespread on the Indian subcontinent that has recently also been identified in North Africa and southern Europe and causes problems in a number of crops including cotton and tomato. The Agrobacterium tumefaciens virulence protein VirE2 has ssDNA binding activity. Nicotiana benthamiana was transformed with a construct for the expression of VirE2 to assess its potential to impart resistance to begomoviruses. Plants of three VirE2 transgenic lines showed attenuated symptoms when infected with either CLCuKoV, CLCuKoV with CLCuMuB or ToLCNDV relative to the severe symptoms induced in non-transformed plants. Presence of the betasatellite was found to reduce the effectiveness of the resistance imparted byVirE2. There was a marked reduction in the accumulation of viral/betasatellite DNA for both viruses as detected by Southern hybridization. The results indicate that VirE2 shows promise in efforts to develop non-conventional, broad spectrum resistance against begomoviruses, being active against monopartite and bipartite begomoviruses. Efforts should now focus on investigating VirE2 resistance in crop plants, with a view to developing commercially useful resistant lines.