Moniliophthora perniciosa contains a range of hosts that allows the categorization of isolates into biotypes: C-biotype is pathogenic to cacao and other Theobroma and Herrania species; S-biotype naturally infects Solanum species and, when inoculated is pathogenic to tomato; and L-biotype that infects liana without provoking visible symptoms. The C- and S-biotypes exhibit primary homothalism, whereas the L-biotype, which is endophytic, is heterothallic, with corss reproduction. Moniliophthora perniciosa contains a tetrapolar genetic sustem to control sexual reproduction, defined by two unlinked loci, A and B, with distinct alleles existing in the population for each locus. The homothallism is characterized by the compatibility between monokaryotic hyphae, genetically identical for the A or B loci to form dikayotic hyphae. The opposite situation, in which the hyphae must present different alleles in A and B results in heterothallism. The fact that the L-biotype is heterothallic, as most of the basidiomycete fungi studied to present, suggest that the transition to homothallism in M. perniciosa (C- and S-biotypes) occurred recently in the evolutionary history of this species. However, it is unknown what the relation of this phenomenon with the evolution of pathogenicity in these biotypes is. With the sequencing of the C-biotype isolate CP02, an insertion of 12 Kb was detected in the A locus, raising the hypothesis that an unequal crossing-over occurred between the two alleles of A in an ancestral heterothallic M. perniciosa that created one single allele containing all the genetic elements necessary for sexual compatibility - at least in this locus. However, more studies are required to confirm or not this hypothesis, especially by searching an insertion in other isolates, including from the S-biotype.Moniliophthora roreri is another cacao pathogen that attacks only pods, causing Moniliasis. Originally, M. roreri was considered from Monilia (Ascomycete), but based in morphological characteristics of the vegetative mycelia, t was transferred to the basidiomycete genus Moniliophthora, created to accommodate it. Cytological analysis indicated that the spores had seual origin (as meiospores), being considered as radically modified basidias with sexual, dispersion and dormancy roles. Such as M. perniciosa, the life cycle of M. roreri involves two pstages: biotrophic and necrotrophic. The conidia/meiospores of M. roreri as germinate produce monokaryotic hyphae, that grow intercellularly and produce the first symptoms. The botrophic hyphae are convoluted and wide, similarly to those from M. perniciosa. At the necrotrophic stage, the hyphae are regular and thin, with a variable number of nuclei, but without clamp connection. The hyphae that cover the pod suffer successive divisions and generate immense number of spores, without the formation of visible basidia. The analysis of the genetc control of sexual reproduction of M. roreri determined the likely genes of the loci A (HD1 and HD2) and B (MrPh4 and STE3_Mr4, respectively the pherormone and its receptor), which are non-functional. The evidences indicate that M. roreri reproduces as clones, but such as M. perniciosa, derives from a tetrapolar heterothallic ancestral. Therefore, the objetice is to investigate the mating-type genetic elements that control sexual reproduction defined by the two unlinked loci A and B, in isolates of the C- and S-biotypes of M. perniciosa. The A locus contain genes that codes for the homeodomain transcription factors HD1 and HD2, whereas the B locus contains precursors of the pherormone and its respective receptors STE3-like.
News published in Agência FAPESP Newsletter about the scholarship: