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Expression divergence measured by transcriptome sequencing of four yeast species.

ABSTRACT: BACKGROUND: The evolution of gene expression is a challenging problem in evolutionary biology, for which accurate, well-calibrated measurements and methods are crucial. RESULTS: We quantified gene expression with whole-transcriptome sequencing in four diploid, prototrophic strains of Saccharomyces species grown under the same condition to investigate the evolution of gene expression. We found that variation in expression is gene-dependent with large variations in each gene's expression between replicates of the same species. This confounds the identification of genes differentially expressed across species. To address this, we developed a statistical approach to establish significance bounds for inter-species differential expression in RNA-Seq data based on the variance measured across biological replicates. This metric estimates the combined effects of technical and environmental variance, as well as Poisson sampling noise by isolating each component. Despite a paucity of large expression changes, we found a strong correlation between the variance of gene expression change and species divergence (R² = 0.90). CONCLUSION: We provide an improved methodology for measuring gene expression changes in evolutionary diverged species using RNA Seq, where experimental artifacts can mimic evolutionary effects.GEO Accession Number: GSE32679.

SUBMITTER: Busby MA

PROVIDER: S-EPMC3296765 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Expression divergence measured by transcriptome sequencing of four yeast species.

Busby Michele A MA Gray Jesse M JM Costa Allen M AM Stewart Chip C Stromberg Michael P MP Barnett Derek D Chuang Jeffrey H JH Springer Michael M Marth Gabor T GT

BMC genomics 20111229

<h4>Background</h4>The evolution of gene expression is a challenging problem in evolutionary biology, for which accurate, well-calibrated measurements and methods are crucial.<h4>Results</h4>We quantified gene expression with whole-transcriptome sequencing in four diploid, prototrophic strains of Saccharomyces species grown under the same condition to investigate the evolution of gene expression. We found that variation in expression is gene-dependent with large variations in each gene's express ...[more]

PMID: 22206443

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Project description:BACKGROUND: The Amazonian rainforest is predicted to suffer from ongoing environmental changes. Despite the need to evaluate the impact of such changes on tree genetic diversity, we almost entirely lack genomic resources. RESULTS: In this study, we analysed the transcriptome of four tropical tree species (Carapa guianensis, Eperua falcata, Symphonia globulifera and Virola michelii) with contrasting ecological features, belonging to four widespread botanical families (respectively Meliaceae, Fabaceae, Clusiaceae and Myristicaceae). We sequenced cDNA libraries from three organs (leaves, stems, and roots) using 454 pyrosequencing. We have developed an R and bioperl-based bioinformatic procedure for de novo assembly, gene functional annotation and marker discovery. Mismatch identification takes into account single-base quality values as well as the likelihood of false variants as a function of contig depth and number of sequenced chromosomes. Between 17103 (for Symphonia globulifera) and 23390 (for Eperua falcata) contigs were assembled. Organs varied in the numbers of unigenes they apparently express, with higher number in roots. Patterns of gene expression were similar across species, with metabolism of aromatic compounds standing out as an overrepresented gene function. Transcripts corresponding to several gene functions were found to be over- or underrepresented in each organ. We identified between 4434 (for Symphonia globulifera) and 9076 (for Virola surinamensis) well-supported mismatches. The resulting overall mismatch density was comprised between 0.89 (S. globulifera) and 1.05 (V. surinamensis) mismatches/100 bp in variation-containing contigs. CONCLUSION: The relative representation of gene functions in the four transcriptomes suggests that secondary metabolism may be particularly important in tropical trees. The differential representation of transcripts among tissues suggests differential gene expression, which opens the way to functional studies in these non-model, ecologically important species. We found substantial amounts of mismatches in the four species. These newly identified putative variants are a first step towards acquiring much needed genomic resources for tropical tree species.

Project description:A fundamental problem in biology is the molecular basis for divergence among related organisms. We have investigated the level of divergence of transcription factor binding sites for two key factors that regulate developmental processes in the budding yeasts. The genomic binding locations for the Ste12 and Tec1 transcription factors in S. cerevisiae, S. mikatae and S. bayanus were mapped by chromatin immunoprecipitation combined with microarrays (chIP chip)1, 2 and compared to one another. While there was a large core network which was conserved in all three species, there were many instances of binding events whose relative levels differ significantly quantitatively in one species relative to another and as well as species-specific binding events. One interesting class of genes were identified that were bound only in S. mikatae and S. bayanus; many of these genes are targets of Ste12 in haploid strains of S. cerevisiae, suggesting that S. cerevisiae has uniquely acquired the ability to differentially regulate these genes in haploid and diploid cells in these species. To extend these studies, the transcriptional network for the Ste12 homologue (Cph1) in Candida albicans was also mapped and compared to the Saccharomyces species. Again, there were several genes bound by Cph1 which are involved in mating in S. cerevisiae, suggesting that the precise delineation between many mating and pseudohyphal targets by Ste12 may be specific to S. cerevisiae. Overall our results demonstrate that transcription binding sites differ faster than gene content indicating that gene regulation at the level of transcription factor binding is likely to be a major mode of evolutionary divergence between related species. We expect that this divergence is essential for the distinct ecological niches inhabited by these organisms. Keywords: chIP-chip ChIP-chip was performed on Ste12 and Tec1 from S. cerevisiae, S. mikatae and S. bayanus in addition to Cph1 from S. cerevisiae. Three biological replicates were performed for each factor in each species with one replicate representing a dye swap.

Project description:BACKGROUND:The interactions of fig wasps and their host figs provide a model for investigating co-evolution. Fig wasps have specialized morphological characters and lifestyles thought to be adaptations to living in the fig's syconium. Although these aspects of natural history are well documented, the genetic mechanism(s) underlying these changes remain(s) unknown. Fig wasp olfaction is the key to host-specificity. The Or83b gene class, an unusual member of olfactory receptor family, plays a critical role in enabling the function of conventional olfactory receptors. Four Or83b orthologous genes from one pollinator (PFW) (Ceratosolen solmsi) and three non-pollinator fig wasps (NPFWs) (Apocrypta bakeri, Philotrypesis pilosa and Philotrypesis sp.) associated with one species of fig (Ficus hispida) can be used to better understand the molecular mechanism underlying the fig wasp's adaptation to its host. We made a comparison of spatial tissue-specific expression patterns and substitution rates of one orthologous gene in these fig wasps and sought evidence for selection pressures. RESULTS:A newly identified Or83b orthologous gene was named Or2. Expressions of Or2 were restricted to the heads of all wingless male fig wasps, which usually live in the dark cavity of a fig throughout their life cycle. However, expressions were widely detected in the antennae, legs and abdomens of all female fig wasps that fly from one fig to another for oviposition, and secondarily pollination. Weak expression was also observed in the thorax of PFWs. Compared with NPFWs, the Or2 gene in C. solmsi had an elevated rate of substitutions and lower codon usage. Analyses using Tajima's D, Fu and Li's D* and F* tests indicated a non-neutral pattern of nucleotide variation in all fig wasps. Unlike in NPFWs, this non-neutral pattern was also observed for synonymous sites of Or2 within PFWs. CONCLUSION:The sex- and species-specific expression patterns of Or2 genes detected beyond the known primary olfactory tissues indicates the location of cryptic olfactory inputs. The specialized ecological niche of these wasps explains the unique habits and adaptive evolution of Or2 genes. The Or2 gene in C. solmsi is evolving very rapidly. Negative deviation from the neutral model of evolution reflects possible selection pressures acting on Or2 sequences of fig wasp, particularly on PFWs who are more host-specific to figs.

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Expression divergence measured by transcriptome sequencing of four yeast species.

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Expression divergence measured by transcriptome sequencing of four yeast species.

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