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Title: Molecular genetics of interactions between Xanthomonas campestris pv. raphani and Arabidopsis thaliana
Author: Horta de Passo, Vânia
ISNI:       0000 0004 6348 7290
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2016
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The major aim of this research was to investigate interactions between the bacterial pathogen Xanthomonas campestris pv. raphani (Xcr) and Arabidopsis thaliana which are largely unexplored as a model pathosystem, and to identify genetic loci conferring resistance to this pathogen. Xcr is genetically close to X. campestris pv. campestris (Xcc) and both pathogens infect common Brassicaceae species including A. thaliana, but cause distinct diseases - leaf spot and black rot, respectively. Phenotypic variation was identified among interactions between 22 A. thaliana accessions of wide geographic origin and Xcr and Xcc strains representing known host genotype specific races. Accessions were identified showing broad resistance and broad susceptibility to multiple Xcr and Xcc strains as well as accessions that differentiate between Xcr races. Genetic mapping of resistance to a strain of Xcr race 2 in a multi-parent recombinant inbred population revealed two major effect loci: RXCR1 at the bottom arm of chromosome 3, and RXCR2 at the bottom arm of chromosome 5. RXCR1 was confirmed by fine-mapping and loss- and gain-of-function experiments, as a single gene encoding a kinase-like protein conferring resistance in the accession Columbia. Columbia is resistant to strains of all three known Xcr races, but RXCR1 is insufficient on its own to explain the broad resistance. A summary of phenotypic and genetic analyses of interactions between Xcr and A. thaliana is presented in a gene-for-gene model. X. campestris strains associated with outbreaks of a leaf spot and blight disease of brassica crops in Mauritius, were characterized. These strains were similar to reference Xcc strains in pathogenicity tests and molecular analyses. The presence of Xcr in these outbreaks was not confirmed. Whole-genome sequencing data was used to identify genes that may contribute to the distinct modes of pathogenesis of Xcr and Xcc as well as variation in host specific races within each pathovar. Genes differentially present/absent between nine Xcr and 23 Xcc strains were identified and include genes predicted/known to encode type III effectors some of which have been previously described to have an effect on Xcc pathogenicity. Candidate avirulence determinants of Xcr and Xcc races were also identified.
Supervisor: Not available Sponsor: Fundação para a Ciência e a Tecnologia
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QR Microbiology