Functional analysis of cacao disease resistance genes

The recent description of the cacao genome sequence led to the identification of a large number of genes implicated in the mechanisms of disease resistance though sequence similarities to known defense genes from other plants¹.  Anchoring of the cacao genome to genetic and QTL maps revealed that a number of the putative defense-related  genes co-localize to QTLs for diseases resistance, providing further evidence that they may involved in the specific mechanisms of pathogen defense.  Using a combination of approaches we have begun to explore the function of some of these genes with a long-term goal to provide knowledge and molecular markers in support of cacao breeding programs.  By expressing cacao genes in Arabidopsis, we have obtained definitive evidence of the role of the TcNPR1 gene and of a related negative regulator, TcNPR3, in the regulation of the plant immune system.  To accelerate our research, we developed a rapid transient assay in cacao leaves, which couples Agro-infiltration as a gene delivery method with a pathogenicity bioassay.  The method has provided further evidence of the function of several candidate defense genes.  The results of this work will be summarized.

1)  The genome of Theobroma cacao. Nature Genetics:  Published online: 26 December 2010 | doi:10.1038/ng.736