Rhodosporidium toruloides is a heterothallic, bipolar, red yeast that belongs to the Sporidiobolales, an order within a major lineage of basidiomycetes, the Pucciniomycotina. In contrast to other basidiomycetes, considerably less is known about the nature of the mating type (MAT) loci that control sexual reproduction in this lineage. Three genes (RHA1, RHA2, and RHA3) encoding precursors of the MAT A1 pheromone (rhodotorucine A) were previously identified and formed the basis for a genome walking approach that led to the identification of additional MAT genes in complementary mating strains of R. toruloides. Two mating type-specific alleles encoding a p21-activated kinase (PAK; Ste20 homolog) were found between the RHA2 and RHA3 genes, and identification in MAT A2 strains of a gene encoding a presumptive pheromone precursor enabled prediction of the structure of rhodotorucine a. In addition, a putative pheromone receptor gene (STE3 homolog) was identified upstream of RHA1. Analyses of genomic data from two closely related species, Sporobolomyces roseus and Sporidiobolus salmonicolor, identified syntenic regions that contain homologs of all the above-mentioned genes. Notably, six novel pheromone precursor genes were uncovered, which encoded, similarly to the RHA genes, multiple tandem copies of the peptide moiety. This suggests that this structure, which is unique among fungal lipopeptide pheromones, seems to be prevalent in red yeasts. Species comparisons provided evidence for a large, multigenic MAT locus structure in the Sporidiobolales, but no putative homeodomain transcription factor genes (which are present in all basidiomycetous MAT loci characterized thus far) could be found in any of the three species in the vicinity of the MAT genes identified.Fungal mating type (MAT) loci are specialized genomic regions that determine cell type identity and coordinate the sexual cycle. Their genetic structure has been relatively sparsely sampled in broad phylogenetic terms, but results of published studies have revealed both conserved features and remarkable diversity in ascomycetes and basidiomycetes (8, 13). A common trait of fungal MAT loci is the presence of genes encoding homeodomain or other classes of transcription factors that control the expression of genes that establish cell type identity and activate sexual development. In basidiomycetes, two major types of MAT loci have so far been recognized (9). The tetrapolar mating system of the corn smut Ustilago maydis and the mushrooms Coprinopsis cinerea and Schizophyllum commune is governed by two small (Ͻ10-kb) unlinked loci: one encodes homeodomain transcription factors (HD1 and HD2 homologs), and the other encodes lipopeptide pheromones and pheromone receptors (STE3 homologs), which mediate intercellular signaling prior to cell fusion and/or sexual development after mating (9). Each locus may be multiallelic, which can result in up to thousands of compatible mating types in certain tetrapolar species. On the other hand, in the bipolar system of the human pathog...
ABSTRACT. Substrate-binding subunits are important components of the solute importation system, known as the osmoprotectant system, which consists of a membrane protein belonging to the ABC superfamily. These molecules recognize specific substrates that have different physiological roles in prokaryotes, i.e., roles that contribute to the survival of these organisms in environments with high concentrations of salt. Using the MEGA software, this study performed a phylogenetic analysis of 431 nucleotide sequences of these subunits, orthologous to each other, collected from the http://www.genome. jp/kegg/ database. This analysis allowed phylogenetic trees to be generated, clearly demonstrating that there was horizontal transfer of some genes through sharing by different organisms. Furthermore, two probable ancestral sequences were generated that showed homology with permeases that transport choline, glycine betaine, and carnitine, which are trimethylamines currently present in various prokaryotes. Therefore, this system probably arose in prokaryotic organisms with the basic function of capturing nutrients, and by performing this basal function and being shared with other organisms, it was fixed in the genome. However, because of prokaryote habitat diversification, this system contributed decisively to the adaptation of these organisms to different environments, especially environments that had a high salt concentration, thus acting as an osmoprotection system, which is how they are currently categorized.
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