Control of tomato-infecting tospoviruses and geminiviruses by transgenic resistance

Thrips-borne ssRNA tospoviruses and whitefly-borne ssDNA geminiviruses seriously threaten tomato production worldwide. Conventional breeding using resistance or tolerance genes for the control of these viruses are normally not sustainable due to the rapid emergence of diverse resistance-breaking virus strains. Hence, transgenic resistance triggered by a modified transgene from these viruses becomes an effective strategy to control these viruses. Transgenic tobacco or tomato plants carrying the N gene, NSm gene or the composite of different N genes of tospoviruses confer high degrees of resistance to the homologous virus; however, the resistance easily can be overcome by heterologous virus strains. Since the RdRp domain of L genes is highly conserved among all tospoviruses, we used the untranslatable L gene conserved region as a transgene for inducing post-transcriptional gene silencing (PTGS) in transgenic lines of Nicotiana benthamiana and tomato. This conferred high levels of complete resistance to 10 different Tospovirus species at the genus level. Disarming the NSs gene (the silencing suppressor and pathogenicity determinant of a tospovirus) by PTGS is regarded as an effective approach to generating transgenic resistance. Our results showed that the NSs fragment can enhance the broad-spectrum resistance conferred by the L gene conserved region to generate high levels of broad-spectrum and durable resistance against distinct tospoviruses in real crops. To solve the problem of geminivirus and tospovirus simultaneously, we constructed a two-T DNA marker-free vector carrying a hairpin of the intergenic region (IGR) of Ageratum yellow vein virus (AYVV; Geminivirus), residing in an intron inserted in an untranslatable N-gene fragment of melon yellow spot virus (MYSV; Orthotospovirus). Transgenic tobacco lines highly resistant to AYVV and MYSV were generated through transcriptional gene silencing (TGS) which occurred in the nucleus and PTGS which occurred in the cytoplasm of cells, respectively. In addition, transgenes against aphid-borne viruses can be introduced to these marker-free transgenic plants to generate super tomato lines with broad-spectrum resistance against insect-borne viruses.