A dual role for calcium oxalate in Theobroma cacao tissues infected by the hemibiotrophic fungus Moniliophthora perniciosa

It has been previously demonstrated that calcium oxalate accumulates on tissues of Theobroma cacao during infection caused by the hemibiotrophic fungus Monilhiopthora. perniciosa. In this work we report that this molecule has an ambiguous role, temporal and genotype-dependent. Susceptible genotype accumulates more calcium oxalate crystals then the resistant one. Conversely, the soluble oxalic acid found on the resistant genotype is a substrate to the oxalate oxidase enzyme, which causes the release of reactive oxygen species (ROS) into the cells, possible early blocking the infection. The opposite has been shown to the susceptible genotype, whereas the later degradation of the oxalic acid released from the dissolution of the druses generates a burst of H2O2 into the tissues, inducing programmed cell death. The levels of ascorbic acid increased during the infection on susceptible genotype, but remained constant on the resistant. The possible origin of the oxalic acid from ascorbic acid is discussed. This contrasting behavior causes the role of oxalic acid to be ambiguous. Indeed, previous works for other species consider either linked to resistance or susceptibility. (Texte integral)