Résumé
Since 1989, the Witches' broom disease due to the pathogenic fungi Crinipellis perniciosa increased in Brazil, the cultivation of cocoa trees and leading to important economical and social changes in the concerned areas such as in the Bahia state. The aim of the research developed in the laboratory is to acquire a good knowledge of the determinism of the interaction between the cocoa tree and the pathogen Crinipellis based on functional genomic studies, and to contribute to the development of effective methods for the genetic improvement of resistance to this disease, so as to create new varieties obtained through a Marker-Assisted Selection (MAS) strategy. We report here studies related to gene expression in meristems of resistant and susceptible cocoa trees inoculated or not with Crinipellis perniciosa spores. Plants were harvested from time zero up to 70 days after inoculation (necrosis symptoms), then used to generate Expressed Sequence Tags (ESTs) by random sequencing. First, we developed a successful and reliable procedure for the isolation of RNA from any cocoa tissues particularly those containing a high content of polyphenols and polysaccharides such as meristems and fruits. Then, we generated two cDNA libraries corresponding to inoculated resistant and susceptible plants. The cDNA libraries were cloned in an expression vector that can also be induced to produce proteins. We randomly sequenced 10 000 ESTs of both libraries. The collection of ESTs thus obtained provide new data about the physiology of the interaction between Theobroma cacao and Crinipellis perniciosa. In a short term we plan to do a functional analyze of some candidate genes which can also be used for mapping, to facilitate introgression strategies and to create new varieties resistant to Crinipellis perniciosa. These data may also be related to research on gene expression of cocoa challenged with other pathogens, such as Phytophthora ssp. (Texte intégral)