Diverse mating phenotypes impact the spread of wtf meiotic drivers in Schizosaccharomyces pombe.

Meiotic drivers are genetic elements that break Mendel's law of segregation to be transmitted into more than half of the offspring produced by a heterozygote. The success of a driver relies on outcrossing (mating between individuals from distinct lineages) because drivers gain their advantage in heterozygotes. It is, therefore, curious that Schizosaccharomyces pombe, a species reported to rarely outcross, harbors many meiotic drivers. To address this paradox, we measured mating phenotypes in S. pombe natural isolates. We found that the propensity for cells from distinct clonal lineages to mate varies between natural isolates and can be affected both by cell density and by the available sexual partners. Additionally, we found that the observed levels of preferential mating between cells from the same clonal lineage can slow, but not prevent, the spread of a wtf meiotic driver in the absence of additional fitness costs linked to the driver. These analyses reveal parameters critical to understanding the evolution of S. pombe and help explain the success of meiotic drivers in this species.

The fission yeast, Schizosaccharomyces pombe, is a haploid organism, meaning it has a single copy of each of its genes. S. pombe cells generally carry one copy of each chromosome and can reproduce clonally by duplicating these chromosomes and then dividing into two cells. However, when the yeast are starving, they can reproduce sexually. This involves two cells mating by fusing together to create a 'diploid zygote', which contains two copies of each gene. The zygote then undergoes 'meiosis', a special type of cell division in which the zygote first duplicates its genome and then divides twice. This results in four haploid spores which are analogous to sperm and eggs in humans that each contain one copy of the genome. The spores will grow and divide normally when conditions improve. The genes carried by each of the haploid spores depend on the cells that formed the zygote. If the two 'parent' yeast had the same version or 'allele' of a gene, all four spores will have it in their genome. However, if the two parents have different alleles, only 50% of the offspring will carry each version. Although this is usually the case, there are certain alleles, called meiotic drivers, that are transmitted to all offspring even in situations where it is only carried by one parent. Meiotic drivers can be found in many organisms, including mammals, but their behavior is easiest to study in yeast. Meiotic drivers known as killers achieve this by disposing of any 'sister' spores that do not inherit the same allele of this gene. This 'killing' can only happen when only one of the 'parents' carries the driver. This scenario is thought to rarely occur in species that inbreed, as inbreeding leads to both gene copies being the same. However, this does not appear to be the case for S. pombe, which contain a whole family of killer meiotic drivers, the wtf genes, despite also being reported to mainly inbreed. To investigate this contradiction, López Hernández et al. isolated several genetically distinct populations of S.pombe. These isolates were grown together to determine how often the each one would outcross (mate with an individual from a different population) or inbreed. The results found that levels of inbreeding varied between isolates. Next, López Hernández et al. used mathematical modelling and experimental evolution analyses to study how wtf drivers spread amongst these populations. This revealed that wtf genes spread faster in populations with more outcrossing. In some instances, the wtf driver was linked to a gene that could harm the population. In these cases, López Hernández et al. found than inbreeding could purge these drivers and stop them from spreading the dangerous alleles through the population. López Hernández et al. establish a simple experimental system to model driver evolution and experimentally demonstrate how key parameters, such as outcrossing rates, affect the spread of these genes. Understanding how meiotic drivers spread is important, as these systems could potentially be used to modify populations important to humans, such as crops or disease vectors.

Assessment of the ptxD gene as a growth and selective marker in Trichoderma atroviride using Pccg6, a novel constitutive promoter.

BACKGROUND: Trichoderma species are among the most effective cell factories to produce recombinant proteins, whose productivity relies on the molecular toolkit and promoters available for the expression of the target protein. Although inducible promoter systems have been developed for producing recombinant proteins in Trichoderma, constitutive promoters are often a desirable alternative. Constitutive promoters are simple to use, do not require external stimuli or chemical inducers to be activated, and lead to purer enzyme preparations. Moreover, most of the promoters for homologous and heterologous expression reported in Trichoderma have been commonly evaluated by directly assessing production of industrial enzymes, requiring optimization of laborious protocols. RESULTS: Here we report the identification of Pccg6, a novel Trichoderma atroviride constitutive promoter, that has similar transcriptional strength as that of the commonly used pki1 promoter. Pccg6 displayed conserved arrangements of transcription factor binding sites between promoter sequences of Trichoderma ccg6 orthologues genes, potentially involved in their regulatory properties. The predicted ccg6-encoded protein potentially belongs to the SPE1/SPI1 protein family and shares high identity with CCG6 orthologue sequences from other fungal species including Trichoderma reesei, Trichoderma virens, Trichoderma asperellum, and to a lesser extent to that of Neurospora crassa. We also report the use of the Pccg6 promoter to drive the expression of PTXD, a phosphite oxidoreductase of bacterial origin, which allowed T. atroviride to utilize phosphite as a sole source of phosphorus. We propose ptxD as a growth reporter gene that allows real-time comparison of the functionality of different promoters by monitoring growth of Trichoderma transgenic lines and enzymatic activity of PTXD. Finally, we show that constitutive expression of ptxD provided T. atroviride a competitive advantage to outgrow bacterial contaminants when supplied with phosphite as a sole source of phosphorus. CONCLUSIONS: A new constitutive promoter, ccg6, for expression of homologous and heterologous proteins has been identified and tested in T. atroviride to express PTXD, which resulted in an effective and visible phenotype to evaluate transcriptional activity of sequence promoters. Use of PTXD as a growth marker holds great potential for assessing activity of other promoters and for biotechnological applications as a contamination control system.

Veni, vidi, vici: the success of wtf meiotic drivers in fission yeast.

Meiotic drivers are selfish DNA loci that can bias their own transmission into gametes. Owing to their transmission advantages, meiotic drivers can spread in populations even if the drivers or linked variants decrease organismal fitness. Meiotic drive was first formally described in the 1950s and is thought to be a powerful force shaping eukaryotic genomes. Classic genetic analyses have detected the action of meiotic drivers in plants, filamentous fungi, insects and vertebrates. Several of these drive systems have limited experimental tractability and relatively little is known about the molecular mechanisms of meiotic drive. Recently, however, meiotic drivers were discovered in a yeast species. The Schizosaccharomyces pombe wtf gene family contains several active meiotic drive genes. This review summarizes what is known about the wtf family and highlights its potential as a highly tractable experimental model for molecular and evolutionary characterization of meiotic drive.

Global transcriptional analysis suggests Lasiodiplodia theobromae pathogenicity factors involved in modulation of grapevine defensive response.

BACKGROUND: Lasiodiplodia theobromae is a fungus of the Botryosphaeriaceae that causes grapevine vascular disease, especially in regions with hot climates. Fungi in this group often remain latent within their host and become virulent under abiotic stress. Transcriptional regulation analysis of L. theobromae exposed to heat stress (HS) was first carried out in vitro in the presence of grapevine wood (GW) to identify potential pathogenicity genes that were later evaluated for in planta expression. RESULTS: A total of 19,860 de novo assembled transcripts were obtained, forty-nine per cent of which showed homology to the Botryosphaeriaceae fungi, Neofusicoccum parvum or Macrophomina phaseolina. Three hundred ninety-nine have homology with genes involved in pathogenic processes and several belonged to expanded gene families in others fungal grapevine vascular pathogens. Gene expression analysis showed changes in fungal metabolism of phenolic compounds; where genes encoding for enzymes, with the ability to degrade salicylic acid (SA) and plant phenylpropanoid precursors, were up-regulated during in vitro HS response, in the presence of GW. These results suggest that the fungal L-tyrosine catabolism pathway could help the fungus to remove phenylpropanoid precursors thereby evading the host defense response. The in planta up-regulation of salicylate hydroxylase, intradiol ring cleavage dioxygenase and fumarylacetoacetase encoding genes, further supported this hypothesis. Those genes were even more up-regulated in HS-stressed plants, suggesting that fungus takes advantage of the increased phenylpropanoid precursors produced under stress. Pectate lyase was up-regulated while a putative amylase was down-regulated in planta, this could be associated with an intercellular growth strategy during the first stages of colonization. CONCLUSIONS: L. theobromae transcriptome was established and validated. Its usefulness was demonstrated through the identification of genes expressed during the infection process. Our results support the hypothesis that heat stress facilitates fungal colonization, because of the fungus ability to use the phenylpropanoid precursors and SA, both compounds known to control host defense.

'Plug and Play' assembly of a low-temperature plasma ionization mass spectrometry imaging (LTP-MSI) system.

Mass spectrometry imaging (MSI) is of high and growing interest in life science research, but the investment for necessary equipment is often prohibitive for small research groups. Therefore, we developed a basic MSI system from low cost 'Plug and Play' components, which are connected to the Universal Serial Bus (USB) of a standard computer. Our open source software OpenMZxy (http://www.bioprocess.org/openmzxy) enables automatic and manual sampling, as well as the recording of position data. For ionization we used a low-temperature plasma probe (LTP), coupled to a quadrupole mass analyzer. The current set-up has a practical resolution of 1mm, and a sampling area of 100×100mm, resulting in up to 10,000 sampling points. Our prototype is easy and economical to adopt for different types of mass analyzers. We prove the usability of the LTP-MSI system for macroscopic samples by imaging the distribution of metabolites in the longitudinal cross-cut of a chili (Capsicum annuum, 'Jalapeño pepper') fruit. The localization of capsaicin in the placenta could be confirmed. But additionally, yet unknown low molecular weight compounds were detected in defined areas, which underline the potential of LTP-MSI for the imaging of volatile and semi-volatile metabolites and for the discovery of new natural products. Biological significance Knowledge about the spatial distribution of metabolites, proteins, or lipids in a given tissue often leads to novel findings in medicine and biology. Therefore, mass spectrometry based imaging (MSI) is becoming increasingly popular in life science research. However, the investment for necessary equipment is often prohibitive for small research groups. We built a prototype with an ambient ionization source, which is easy and economical to adopt for different types of mass analyzers. Therefore, we hope that our system contributes to a broader use of mass spectrometry imaging for answering biological questions.