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PhD defended january 17th, 2012
Direction: Maria Manzanares-Dauleux & Eric Grenier

abstract:

In order to control the potato cyst nematode, Globodera pallida,using resistant varieties is now advocated. Nevertheless, most of the resistance genes, including the major gene Gpa2, are effi cient only against a limited number of nematode populations. Moreover Gpa2 needs the presence of a cofactor - RanGAP2 - to recognize the nematode avirulence protein coded by the Gp-Rbp-1 gene and to trigger the plant defence mechanisms. The present work aims to characterize the efficiency spectrum of Gpa2 against G. pallida populations from Europe and from South America (the native area of this nematode) and to describe the molecular and functional variability of Gp-Rbp-1 and RanGAP2. Our goals were to identify the Gp-Rbp-1 polymorphisms affecting the outcome of the interaction with Gpa2 and the polymorphisms in RanGAP2 that can be used to expand the range of G. pallida populations controlled by Gpa2. We have shown that susceptibility of a potato cultivar expressing Gpa2 to a G. pallida population could not be exclusively explained by the frequency of avirulent Gp-Rbp-1 variants in this nematode population. Furthermore, among the eight sites of Gp-Rbp-1 found under positive selection, the sole variation at amino acid position 187 (proline/serine) remained suffi cient to explain the recognition of GP-RBP-1 by GPA2. Despite numerous sites found to have evolved under purifying selection, RanGAP2 have two polymorphic sites (amino acids 106 and 237) and one insertion/deletion of interest. Variability observed at these sites do not enable the recognition of virulent variants (non-recognized) of GP-RBP-1 by GPA2 but seems to affect intensity of the hypersensitive response triggered by the recognition of avirulent variants of Gp-Rbp-1 by GPA2.