MATING-TYPE LOCUS IN CITRUS-ASSOCIATED Phyllosticta SPECIES

To date, there are eight known Phyllosticta species associated with various citrus hosts, either as pathogens (e. g. P. citricarpa as the causative agent of Citrus Black Spot) or endophytes (e. g. P. citribraziliensis associated with Citrus sp.). Despite the morphological similarities, these species present different ranges of host and differ in their biology and ecology. One important aspect of the biology of Phyllosticta species is the system of sexual reproduction. For P. citricarpa, for example, sexual reproduction is essential in the epidemiology of CBS disease, and recently it was described as heterothallic. On the other hand, P. capitalensis, P. paracapitalensis and P. citrichinaensis are known to be homothallic, due to the ascospores production in pure cultures. For P. citriasiana, P. citribraziliensis and P. paracitricarpa sexual structures were not observed in laboratory conditions, suggesting the possibility of heterothallism. Thus, to investigate this hypothesis, we searched the mating-type locus in the genomes of citrus-associated Phyllosticta species available at JGI Genome Portal. Nucleotide sequences of P. citricarpa LGMF78 DNA lyase (KX077256), MAT 1-1-1 (KU852493), MAT 1-1-4 (KU845503) and P. citricarpa LGMF5 MAT 1-2-1 (KU845489) and MAT 1-2-5 (KU845519) genes were used as template for a local BLASTn search in all genomes using BioEdit software. For all species, DNA lyase was located in the flanking region of the mating-type genes, as observed for many ascomycetes. P. capitalensis and P. citrichinaensis presented both MAT 1-1-1 and MAT 1-2-1 in the mating-type locus, in accordance with the homothallism already observed in cultures. P. citribraziliensis and P. citriasiana presented only MAT 1-1-1, P. paracitricarpa and P. citricarpa presented only MAT 1-2-1. These results suggest P. citribraziliensis, P. citriasiana and P. paracitricarpa to be heterothallic, similar to what is observed to P. citricarpa, and in accordance with the lack of self-fertility in laboratory cultures. In addition, this information contributes to the understanding of the association of Phyllosticta species with citrus under an evolutionary approach. Further studies evaluating other Phyllosticta spp. isolates to characterize the opposite mating-types for the heterothallic species are suggested. Such approaches could either facilitate crossing-studies as well as promote better understanding of mechanisms involved in ascospores production and sexual cycle.