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Title: A molecular genetic analysis of resistance to poleroviruses in sugar beet and oilseed rape
Author: Gallagher, Eileen Wallace
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2013
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Beet mild yellowing virus (BMYV) and Turnip yellows virus (TuYV) are both poleroviruses that cause significant reduction in the yields of sugar beet and oilseed rape respectively. Both viruses are transmitted by the aphid vector Myzus persicae. Current control methods rely heavily on the use of insecticides for controlling the aphids which can spread these viruses to a wide range of host plants. Recent EU guidelines have tightened control on the use of some of these pesticides, meaning it is becoming increasingly important to find alternative control methods. It is widely agreed in the scientific community, that the best control method would be to generate durable genetically resistant crop plants. In order to achieve this gene targets, either for active or passive resistance, would need to be identified. This study has built on a project that identified a naturally BMYV resistant A. thaliana ecotype, Sna-1. Crosses of the susceptible ecotype (Col-0) to the resistant ecotype Sna-1 identified the resistance as ‘passive’, where susceptibility was dominant, and conditioned by a monogenic trait. This study began by characterising the gene responsible for susceptibility by bulked segregant analysis and AFLP™. This identified a region of ca. 5Mbp region on A. thaliana chromosome 4. This region contains the Arabidopsis elongation initiation factor 4E (eIF4E) gene which has already been implicated in susceptibility to other viruses. This gene has frequently been shown to be important for viral infection in plants, and naturally occurring mutations can result in resistance to other viruses. Further investigation revealed a 12 bp duplicated sequence in the Sna-1 eIF4E allele, located in a region that encodes the cap-binding pocket of eIF4E. The same region has been shown to be required for virus infection in other species. Infections were therefore carried out using mutants in this gene, using TAS-ELISA. Previously susceptible Col-0 plants containing a T-DNA insert, or EMS point mutations in the eIF4E gene were found to be resistant to BMYV infection. Functional complementation with the Col-0 eIF4E allele into a stock that contained Sna-1 eIF4E resulted in susceptibility to BMYV, confirming its role as a susceptibility factor. As BMYV and TuYV are closely related viruses it was hypothesised they would share a similar infection strategy. The mutation in eIF4E was not enough to prevent virus infection, and the method of infection of the UK-BB TuYV isolate remains to be elucidated as infection studies in mutants with defective components of the eukaryotic translation initiation factors, including eIF(Iso)4E gene, has so far failed to identify any requirements for UK-BB TuYV infection. Several T-DNA insertion lines in the eIF(iso)4E gene were tested but it was not possible to verify that any of these lines were true knock-outs. However, the molelcular tools for future verification have been developed. A recent report has implicated eIF(iso)4G components in TuYV infection of Arabidopsis but this result could not be repeated in this study. Further study is required to fully understand the mode of infection of both viruses. It is expected that the identification of essential host genes required for virus infection will aid in the breeding of genetically resistant crops, and reduce the current dependence on harmful pesticides.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available