Control of Turnip yellows virus: Assessing impact on oilseed rape quality traits and dissecting circulative transmission by aphids
Abstract Turnip yellows virus (TuYV) is one of the most significant viral diseases of oilseed rape and may be one of main reasons why commercial oilseed rape crops do not reach their genetic potential. TuYV is transmitted by aphids, sap-sucking hemipteroid insects, and the green peach aphid (GPA) is the predominant vector. TuYV can reduce oilseed rape yield by up to 26% in the UK and may also affect oil quality. Current control measures rely on insecticides; however, changing legislation and reduced effectiveness necessitate novel approaches to virus control. In this thesis, the impact of TuYV on the UK commercial oilseed rape crop was established and sources of partial resistance to TuYV and aphids were investigated. TuYV reduces yield and has a subtle impact on seed physiology including small changes to fatty acid profiles and glucosinolate content. Furthermore, these changes appear to be genotype-dependent and not as a result of virus accumulation in the plant. To learn more about TuYV transmission by aphids, a novel, functional-genomics tool was developed to silence aphid genes by plant-mediated RNA interference (PMRi). Highly specific protein interactions between virus particles and aphid proteins are critical determinants of circulative transmission, a process whereby virus particles can move between aphid cell layers. However, the aphid components underlying these processes are poorly understood. As the GPA Rack1 protein has been implicated in transcytosis of TuYV particles across the aphid gut barrier, PMRi was used to dissect its role in the circulative transmission process. This revealed that Rack1 may have a direct role in TuYV acquisition by GPA. This work further demonstrates the potential of PMRi as a postgenomics tool in aphids and similar insects, but also as a direct means of aphid and/or virus control. These contrasting research strategies have provided a two-pronged approach towards improving TuYV control.
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