Dataset Information

The spread of a transposon insertion in Rec8 is associated with obligate asexuality in Daphnia.

ABSTRACT: Although transitions from sexual to asexual reproduction are thought to have important evolutionary consequences, little is known about the mechanistic underpinnings of these changes. The cyclical parthenogen Daphnia pulex is a powerful model in which to address these issues because female-limited meiosis suppression can be transmitted to sexual individuals via males, providing the opportunity for genetic dissection of the trait. A previous study identified genomic regions differentiating obligately asexual females from their sexual counterparts, and a candidate gene within one such region, encoding the meiotic cohesin Rec8, is the subject of this investigation. The D. pulex genome contains three Rec8 loci, all of which are quite polymorphic. However, at one of the loci, all obligately asexual clones carry an allele containing an identical upstream insertion of a transposable element as well as a frameshift mutation, both of which are completely absent from sexual lineages. The low level of variation within the insertion allele across all asexual lineages suggests that this element may be in the process of spreading through the species, and abrogation or modification of Rec8 function is possibly responsible for converting meiotically reproducing lineages into obligate asexuals.

SUBMITTER: Eads BD

PROVIDER: S-EPMC3271927 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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The spread of a transposon insertion in Rec8 is associated with obligate asexuality in Daphnia.

Eads Brian D BD Tsuchiya Dai D Andrews Justen J Lynch Michael M Zolan Miriam E ME

Proceedings of the National Academy of Sciences of the United States of America 20120103 3

Although transitions from sexual to asexual reproduction are thought to have important evolutionary consequences, little is known about the mechanistic underpinnings of these changes. The cyclical parthenogen Daphnia pulex is a powerful model in which to address these issues because female-limited meiosis suppression can be transmitted to sexual individuals via males, providing the opportunity for genetic dissection of the trait. A previous study identified genomic regions differentiating obliga ...[more]

PMID: 22215604

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Project description:Gene essentiality studies have been performed on numerous bacterial pathogens, but essential gene sets have been determined for only a few plant-associated bacteria. Pseudomonas protegens Pf-5 is a plant-commensal, biocontrol bacterium that can control disease-causing pathogens on a wide range of crops. Work on Pf-5 has mostly focused on secondary metabolism and biocontrol genes, but genome-wide approaches such as high-throughput transposon mutagenesis have not yet been used for this species. In this study, we generated a dense P. protegens Pf-5 transposon mutant library and used transposon-directed insertion site sequencing (TraDIS) to identify 446 genes essential for growth on rich media. Genes required for fundamental cellular machinery were enriched in the essential gene set, while genes related to nutrient biosynthesis, stress responses, and transport were underrepresented. The majority of Pf-5 essential genes were part of the P. protegens core genome. Comparison of the essential gene set of Pf-5 with those of two plant-associated pseudomonads, P. simiae and P. syringae, and the well-studied opportunistic human pathogen P. aeruginosa PA14 showed that the four species share a large number of essential genes, but each species also had uniquely essential genes. Comparison of the Pf-5 in silico-predicted and in vitro-determined essential gene sets highlighted the essential cellular functions that are over- and underestimated by each method. Expanding essentiality studies into bacteria with a range of lifestyles may improve our understanding of the biological processes important for bacterial survival and growth.IMPORTANCE Essential genes are those crucial for survival or normal growth rates in an organism. Essential gene sets have been identified in numerous bacterial pathogens but only a few plant-associated bacteria. Employing genome-wide approaches, such as transposon insertion sequencing, allows for the concurrent analyses of all genes of a bacterial species and rapid determination of essential gene sets. We have used transposon insertion sequencing to systematically analyze thousands of Pseudomonas protegens Pf-5 genes and gain insights into gene functions and interactions that are not readily available using traditional methods. Comparing Pf-5 essential genes with those of three other pseudomonads highlights how gene essentiality varies between closely related species.

Project description:Many plant-associated bacteria have the ability to positively affect plant growth and there is growing interest in utilizing such bacteria in agricultural settings to reduce reliance on pesticides and fertilizers. However, our capacity to utilize microbes in this way is currently limited due to patchy understanding of bacterial-plant interactions at a molecular level. Traditional methods of studying molecular interactions have sought to characterize the function of one gene at a time, but the slow pace of this work means the functions of the vast majority of bacterial genes remain unknown or poorly understood. New approaches to improve and speed up investigations into the functions of bacterial genes in agricultural systems will facilitate efforts to optimize microbial communities and develop microbe-based products. Techniques enabling high-throughput gene functional analysis, such as transposon insertion sequencing analyses, have great potential to be widely applied to determine key aspects of plant-bacterial interactions. Transposon insertion sequencing combines saturation transposon mutagenesis and high-throughput sequencing to simultaneously investigate the function of all the non-essential genes in a bacterial genome. This technique can be used for both in vitro and in vivo studies to identify genes involved in microbe-plant interactions, stress tolerance and pathogen virulence. The information provided by such investigations will rapidly accelerate the rate of bacterial gene functional determination and provide insights into the genes and pathways that underlie biotic interactions, metabolism, and survival of agriculturally relevant bacteria. This knowledge could be used to select the most appropriate plant growth promoting bacteria for a specific set of conditions, formulating crop inoculants, or developing crop protection products. This review provides an overview of transposon insertion sequencing, outlines how this approach has been applied to study plant-associated bacteria, and proposes new applications of these techniques for the benefit of agriculture.

Dataset Information

The spread of a transposon insertion in Rec8 is associated with obligate asexuality in Daphnia.

Publications

The spread of a transposon insertion in Rec8 is associated with obligate asexuality in Daphnia.

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