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The dissection and identification of resistance genes controlling extreme disease resistance in brassica

Primary Supervisor: Professor John Walsh, School of Life Sciences

Secondary supervisor: Dr Guy Barker, Warwick, Dr Charlotte Nellist, NIAB Cambridge University Crop Research

PhD project title: The dissection and identification of resistance genes controlling extreme disease resistance in brassica

University of Registration: University of Warwick

Project outline:

Plant viruses are responsible for approximately half of the emerging plant diseases worldwide and cause severe yield losses in commercial crops. Climate change and the withdrawal of insecticide active ingredients will exacerbate plant virus disease problems in the future. Plant resistance is the most environmentally friendly, energy efficient and promising approach to virus control.

Virus resistance is often achieved by intrinsic plant pathogen defence system. Infection depends on the interaction of viral factors with plant host proteins. Most plant pathogen resistances known depend on dominant R genes. However, such resistances are predominantly strain-specific.

This research project aims to dissect the interactions between a viral pathogen and its host plant to identify the plant genes involved and their interactions in order to inform intelligent ways of combining the genes to develop more durable resistances.

We have identified a number of resistances to the economically important plant virus, turnip mosaic virus. The resistances are extreme and no virus replication has been detected and no micro-hypersensitive response (HR) has been seen (Fig. 1).

The resistances are dominant and four genes (TuRB01, TuRB03, TuRB04 and TuRB05) have been mapped in B. napus and a further gene postulated (“TuRB06”) that are associated with different strain-specific extreme resistances. TuRB04 and TuRB05 work in concert to provide extreme resistance to all pathotype 1 and all pathotype 3 isolates of TuMV. TuRB01 provides extreme resistance to all pathotype 1 isolates and is postulated to require a second gene “TuRB06”. TuRB03 provides resistance to some, but not all pathotype 4 isolates and the gene-for-gene hypothesis dictates the presence of a second, as yet, unidentified gene.

Figure 1. Oilseed rape (Brassica napus) plants possessing turnip mosaic virus (TuMV) resistance gene TuRB01 (left) and lacking TuRB01 (right) following challenge with TuMV.

We have also identified the viral proteins involved in overcoming the TuRB0 resistance genes (Fig. 2).

Fig. 2. The proteins of turnip mosaic virus indicating the Protein 3 (P3) and Cytoplasmic Inclusion (CI) proteins involved in overcoming

It is not known why some resistance genes confer extreme resistance rather than the HR associated with most plant resistance genes. In collaboration with colleagues in Canada, we have cloned the TuRB01 gene candidate and this has allowed us to postulate a hypothesis to explain the nature of extreme resistance to plant viruses.

The PhD will focus on identifying the TuRB0 genes and addressing the hypothesis on the nature of extreme resistance.

References:

  1. Walsh, J.A. & Jenner, C.E. (2002). Turnip mosaic virus and the quest for durable resistance. Molecular Plant Pathology 3, 289-300.
  2. Jenner, C.E., Wang, X., Tomimura, K., Ohshima, K., Ponz, F. & Walsh, J.A. (2003). The dual role of a potyvirus protein of Turnip mosaic virus as a symptom determinant and an avirulence determinant in brassicas. Molecular Plant-Microbe Interactions 16, 777-784.
  3. Hughes, S.L., Hunter, P.J., Sharpe, A.G., Kearsey, M.J., Lydiate, D.J. & Walsh, J.A. (2003). Genetic mapping of a novel Turnip mosaic virus resistance gene in Brassica napus. Theoretical and Applied Genetics 107, 1169-1173.
  4. Tomimura, K., Gibbs, A.J., Jenner, C.E., Walsh, J.A. & Ohshima, K. (2003). The phylogeny of Turnip mosaic virus; comparisons of thirty-eight genomic sequences reveal a Eurasian origin and a recent ‘emergence’ in East Asia. Molecular Ecology 12, 2099-2111
  5. Nellist, C.F., Ohshima, K., Ponz, F. & Walsh, J.A. (in press). Turnip Mosaic Virus, a Virus for All Seasons. Annals of Applied Biology

BBSRC Strategic Research Priority: Sustainable Agriculture and Food: Plant and Crop Science; Renewable Resources and Clean Growth: Bio-energy; Understanding the Rules of Life: Microbiology & Plant Science; Integrated Understanding of Health: Diet and Health

Techniques that will be undertaken during the project:

  • Virus detection via enzyme-linked immunosorbent assay (ELISA) and RT-PCR
  • QTL analysis
  • PCR and plant gene sequencing
  • Gene cloning
  • Plant transformation

Contact: Professor John Walsh, University of Warwick