Project description:Comparative time-series expression analysis of growth curves through carbon depletion in the ascomycete yeasts Each of the following species-specific, growth curve derived samples competitively hybed to their own mid-log samples: lag phase, late log, diauxic shift, post-shift, plateau
Project description:Comparative time-series expression analysis of growth curves through carbon depletion in the ascomycete yeasts. Each of the following species-specific, growth curve derived samples competitively hybed to their own mid-log samples: lag phase, late log, diauxic shift, post-shift, plateau.
Project description:Divergence in gene regulation can play a major role in evolution. Here, we used a phylogenetic framework to measure mRNA profiles in 15 yeast species from the phylum Ascomycota and reconstruct the evolution of their modular regulatory programs along a time course of growth on glucose over 300 million years [corrected]. We found that modules have diverged proportionally to phylogenetic distance, with prominent changes in gene regulation accompanying changes in lifestyle and ploidy, especially in carbon metabolism. Paralogs have significantly contributed to regulatory divergence, typically within a very short window from their duplication. Paralogs from a whole genome duplication (WGD) event have a uniquely substantial contribution that extends over a longer span. Similar patterns occur when considering the evolution of the heat shock regulatory program measured in eight of the species, suggesting that these are general evolutionary principles. DOI:http://dx.doi.org/10.7554/eLife.00603.001.
Project description:The standard genetic code is almost universal, and the evolutionary factors that caused a few organisms to deviate from it are poorly understood. We report that three independent changes of the genetic code occurred during the evolution of budding yeasts, each of which was a reassignment of the codon CUG from leucine to another amino acid. We identify five major yeast clades that differ by translating CUG as either Ser (2 clades), Ala (1 clade), or Leu (2 clades). The newly discovered Ser2 clade is in the final stages of transition from one genetic code to another. It appears to use only a novel tRNASer (tSCAG) to translate CUG codons, but the gene for the ancestral tRNALeu (tLCAG) is still intact in most species in the clade, consistent with the ‘ambiguous intermediate’ theory. We propose that the three parallel changes of the genetic code in yeasts were not driven by natural selection in favor of their effects on the proteome, but by selection to eliminate the ancestral tLCAG, possibly in response to a killer toxin.
Project description:Unusually among fungi, Saccharomyces cerevisiae is able to grow in environments containing almost no oxygen. A major feature of its response to hypoxia is a transition in expression from aerobic to hypoxic genes, which often code for duplicated isoforms of the same protein. In aerobic conditions, expression of the hypoxic gene set is repressed by the HMG domain protein Rox1. Here, we examined the evolution of ROX1 and related genes in the subphylum Saccharomycotina and find that a substantial reorganization of hypoxic gene regulation occurred during yeast evolution. S. cerevisiae lost ROX2, an ancient paralog of ROX1, which is almost universally present in other yeast species. ROX2 is orthologous to Candida albicans RFG1, a regulator of filamentous growth. Many yeasts, such as Candida glabrata, lack ROX1 and contain only ROX2. Others such as Naumovozyma castellii retain both genes. Although the ancestral function of ROX2 is uncertain, we find that it is not a regulator of hypoxic genes except in C. glabrata where it has taken over this function from the absent ROX1. We also find that N. castellii has a greatly attenuated transcriptional response to hypoxia as compared to other species, but that the ergosterol pathway which is normally induced by hypoxia can be induced by cobalt chloride stress in N. castellii.