Date Published: September 17, 2008
Publisher: Public Library of Science
Author(s): Daniel R. Matute, Lina M. Quesada-Ocampo, Jason T. Rauscher, Juan G. McEwen, John W. Taylor
Abstract: Paracoccidioides brasiliensis is a dimorphic fungus that is the causative agent of paracoccidioidomycosis, the most important prevalent systemic mycosis in Latin America. Recently, the existence of three genetically isolated groups in P. brasiliensis was demonstrated, enabling comparative studies of molecular evolution among P. brasiliensis lineages. Thirty-two gene sequences coding for putative virulence factors were analyzed to determine whether they were under positive selection. Our maximum likelihood–based approach yielded evidence for selection in 12 genes that are involved in different cellular processes. An in-depth analysis of four of these genes showed them to be either antigenic or involved in pathogenesis. Here, we present evidence indicating that several replacement mutations in gp43 are under positive balancing selection. The other three genes (fks, cdc42 and p27) show very little variation among the P. brasiliensis lineages and appear to be under positive directional selection. Our results are consistent with the more general observations that selective constraints are variable across the genome, and that even in the genes under positive selection, only a few sites are altered. We present our results within an evolutionary framework that may be applicable for studying adaptation and pathogenesis in P. brasiliensis and other pathogenic fungi.
Partial Text: The neutral theory of evolution states that most evolutionary change at the molecular level is caused by the fixation of neutral alleles through random genetic drift . Nonetheless, it is the impact of natural selection on genomic evolution that is of interest if we wish to understand patterns of adaptive evolution by distinguishing between selectively neutral and non-neutral evolutionary change, and relate this change to the biology and history of the organism. The arms race between hosts and their pathogens is a particularly useful system for relating potentially non-neutral evolutionary change to the biology and history of the organisms , because of the role natural selection plays in maintaining or fixing different alleles in both host and pathogen populations .