Exploiting eIF4E-based and associated broad-spectrum recessive resistance to potyviruses in dicots and monocots.

The project is a collaboration between Warwick HRI working on the dicotyledonous brassica plants and Rothamsted Research working on the monocotyledonous plants barley. The main aim is to: exploit sources of recessive eIF4E-based resistance to potyviruses in these plants. The involvement of the plant gene eIF4E in the life-cycle of viruses was first discovered in experiments on Turnip mosaic virus (TuMV, a potyvirus) and Arabidopsis. Subsequently it was found that the genes eIF4E or its isoform (eIF(iso)4E) are responsible for natural resistance to potyviruses in a range of crop types. The basis of the resistance is that potyviruses require one of these genes in order to complete their life-cycle. It is known that plants with specific alterations in these genes that affect the binding between the plant protein it codes and a viral protein (VPg) are resistant to infection. We have shown that eIF4E is associated with resistance to potyviruses in brassica and barley. The resistances described so far in other plant types involving eIF4E alone are not effective against all strains of the particular potyvirus. However, we have shown that in a brassica, eIF4E in combination with another gene (retr01), confers resistance against all strains of the potyvirus (TuMV). Other genes are involved in the interaction between the viral VPg protein and eIF4E, these include a the very similar gene eIF(iso)4E and other associated genes (eIF4G, eIF4A and isoforms of these). By studying the natural variation in the eIF4E and eIF(iso)4E genes from resistant and susceptible Brassica rapa and barley lines we aim to find new sources of resistance and understand the mechanism of the resistance. We will screen a collection of plants representing 95% of the genetic variation available within the brassica species and a barley diversity panel consisting of up to 800 landraces. Those plants that differ within the eIF4E gene will be tested with informative isolates of the potyviruses to check for resistance/susceptibility. Any eIF4E or eIF(iso)4E variants conferring resistance will be sequenced. This will be supported by looking at plants that have been mutated with chemicals to identify other novel changes in eIF4E and eIF(iso)4E alleles. Lines with such changes will be tested for resistance to a panel of BaMMV and BaYMV isolates. The aim is to identify forms of eIF4E that confer resistance that is durable to all (or most) virus isolates. Using the crystal structures available for eIF4E a model will be generated for eIF4E from barley and B. rapa. Natural and chemically-induced changes in the building blocks (amino acids) of the eIF4E associated with virus resistance in barley and B. rapa will be mapped on the 3D model of the normal eIF4E proteins. The effect of the changes on the potential ability of barley and B. rapa eIF4E to bind to the viral VPg protein will then be investigated. The outcome of this work will be the prediction of superior resistance genes of barley and B. rapa eIF4E for deployment in breeding. A gene retr01 which in combination with eIF4E confers the broad-spectrum resistance to TuMV in B. rapa will be fine mapped to identify the gene's position in the plant genome. The sequence of the gene will be used to search databases to predict its function, understand the mechanism of the broad-spectrum resistance and how retr01 might interact with eIF4E. Based on the best sources of virus resistance in brassicas and barley, changes associated with the genes conferring resistance will be used to design assays which can be used by breeders to incorporate the resistances into their elite breeding stocks by normal breeding methods (crossing). The project will provide an understanding of the scientific basis of the broad-spectrum resistance. Once the mechanism is understood it should be possible to deploy such resistance in a wide range of economically important crop species.

The Potyviridae is the largest family of plant viruses in the world and cause some of the most important virus diseases of crops in the world. Plant resistance to viruses is the only reliable and sustainable means of control. Potyviruses seem to require the eukaryotic translation initiation factor 4E (eIF4E plant gene) for successful multiplication in the host. Incompatibility between variants of eIF4E genes and the potyvirus VPg has been found to be the basis of natural resistance to potyviruses in several species. eIF4E-based resistance is frequently strain-specific. This project aims to look for natural allelic variation in eIF4Ee within brassica and barley. Chemically induced allelic variants of eIF4E identified using barley TILLING populations currently available will increase the likelihood of finding novel variants capable of conferring resistance to potyviruses. Using these approaches and through modelling the likely effect of the different alleles on the known binding sites within the protein from both monocots and dicots we aim to identify and predict those likely to confer resistance to resistance breaking strains of the potyviruses. Other genes have been identified that have a role in the eukaryotic initiation complex (EIC) including eIF(iso)4E which has also been shown to be capable of conferring resistance. Allelic variation and possible associated resistance in this gene will also be investigated. In B. rapa we have already mapped a second gene (retr01) which with eIF4Ee confers broad-spectrum resistance to TuMV. This presents the opportunity to develop more durable resistance. By identifying this gene we will be able to determine if it is involved in the EIC and whether it interacts with eIF4Ee to confer broad-spectrum resistance. Discovery of the gene/s underlying broad-spectrum potyvirus resistance associated with eIF4E and markers for these provides the exciting possibility of developing durable potyvirus resistance in a wide range of crops.