Résumé
Witches' broom disease, caused by the fungus Moniliophthora perniciosa, is one of the main diseases of cacao (Theobroma cacao L.) and is responsible to severe economic losses in the production areas. Recently, expressed sequence tags (ESTs) from cacao-M. perniciosa interaction were obtained and differentially defense-related genes expressed during the cacao-M. perniciosa interaction were identified. Among them, a Selenium-Binding Protein (TcSBP) was found. In other organisms, SBP genes are related to the increase of plant defenses against abiotic and biotic stresses; in rice the SBP gene was successfully used to increase the plant resistance to Magnaporthe grisea by plant transformation. Here, in silico characterization and expression analysis of TcSBP were developed. Search on the Cacao Genome Database revealed the presence of only one SBP sequence of 4774 pb in length located on the chromosome 4. The TcSBP ORF is 1431 bp in length and encodes a protein of 476 amino acids which does not contain any signal peptide. Prediction of possible post-translational events allowed the identification of several glycosylation, phosphorylation and acetylation sites. The comparison of TcSBP sequence with SBP from other organisms using the BLASTP tool revealed identity from 62% to 91% and allowed the identification of specific conserved regions. The expression analysis of TcSBP in meristems of cacao plantlets varieties Catongo (susceptible) and TSH1188 (resistant to M. perniciosa), inoculated or not with M. perniciosa, was obtained by RT-qPCR using 3 biological and 3 experimental replicates. qPCR analysis of TcSBP gene was conducted using the standard settings of the ABI PRISM 7500 and the System of Sequence Detection software. The TcSBP relative expression was analyzed with the comparative Ct method (2-??Ct) using malate dehydrogenase and actin as endogenous reference genes, and noninoculated plants (control) as calibrator. The relative expression of TcSBP was significantly increased 8 and 15 days after inoculation in the resistant variety TSH1188 compared to susceptible Catongo. These data suggest the possible role of TcSBP in cacao resistance to M. perniciosa. This study is the first step to better understand the role of TcSBP in cacao resistance as well as for the development of control strategies of the witches' broom disease (e.g. using plant transformation). Work supported by FAPESB, CAPES, EMBRAPA, CNPq, FINEP/Renorbio and CIRAD. (Texte intégral)