Identification of Theobroma cacao genes differentially expressed during Phytophthora megakarya infection

• We improve molecular mechanisms involved in Theobroma cacao resistance to Phytophthora.
• Comparison of promoter sequences of protease inhibitor genes.
• Functional genomic and differential expression analysis.

Cocoa black pod caused by Phytophthora is one of the most serious diseases affecting cocoa production. This project set out was to improve our knowledge of the molecular mechanisms involved in Theobroma cacao resistance. We performed a transcriptional screening using macroarrays containing 89 ESTs from subtractive libraries enriched with genes differentially expressed in response to T. cacao/Phytophthora interactions. A gene expression analysis revealed the induction of genes involved in stress signal transduction, general and specific defence genes and genes involved in hormone signalling pathways. RT-qPCR showed that the level expression of two genes in the resistant plant was higher during the first eight hours after pathogen inoculation. Three genes from a family encoding a protease inhibitor displayed different levels of expression depending on resistant and susceptible T. cacao clones. A comparison of promoter sequences revealed a motif present only in genes that were up-expressed in the resistant plant.