Biology subjects

Bulach, T.

Publications and source records attributed to Bulach, T..

3 recordsLinked to original sources

bioRxiv2024

Sequence-based genome-wide association studies reveal the polygenic architecture of Varroa destructor resistance in Western honey bees Apis mellifera

Honey bees, Apis mellifera, have experienced the full impacts of globalisation, including the recent invasion by the parasitic mite Varroa destructor which has become one of the main causes of colony losses worldwide. Despite its lethal effects, some colonies have developed defence strategies conferring colony resistance and, assuming non-null heritability, selective breeding of naturally resistant bees could be a sustainable way to fight infestations. Here we report on the largest genome-wide association study performed on honey bees to understand the genetic basis of multiple phenotypes linked to varroa resistance. This study was performed on whole genome sequencing of more than 1,500 colonies belonging to different ancestries and combined in a meta-analysis. Results show that varroa resistance is polygenic. A total of 60 genetic markers were identified as having a significant impact in at least one of the tested populations pinpointing several regions of the honey bee genome. Our results also support strategies for genomic selection in honey bee breeding.

genetics↗

bioRxiv2022

Comparative phylotranscriptomics reveals a 110 million years-old symbiotic program

Symbiotic interactions have structured past and present ecosystems and shaped the evolution of life. As any trait, the symbiotic state observed in extant species builds on ancestral and conserved features, and lineage-specific innovations. From these mixed origins, defining the ancestral state of symbiotic associations is challenging although it is instrumental for understanding how symbiotic abilities emerge from non-symbiotic states. Here we aimed at reconstructing the intermediate steps leading to the root-nodule nitrogen-fixing symbiosis (RNS) observed in some extant flowering plants. For this, we compared the transcriptomic responses of nine host plants in response to symbiotic bacteria. We included the mimosoid legume Mimosa pudica for which we assembled a chromosome-level genome and generated the transcriptomic response to experimentally evolved bacterial symbionts. With this dataset, we reconstructed the ancestral RNS transcriptome, composed of most already described symbiotic genes together with hundreds of novel candidates. We found that the response to the chemical signals produced by the symbiont, nodule organogenesis and nitrogen-fixation are predominantly linked to ancestral responses, although these traits have diversified in the different nitrogen-fixing lineages. We detected a clear signature of recent and convergent evolution for the ability to release intracellular symbiosomes in two legume lineages, exemplified by the expression of different classes of small proteins in each group, potentially leading to the convergent gain of symbiotic evolutionary stability. Our findings demonstrate that most of the novelties for RNS were mostly in place in the most recent common ancestor of the RNS-forming species that lived on Earth 110 million years ago. Graphical abstractA little graphical/nice phylogeny with nodes of interest HighlightsO_LIWe sequenced a high-quality genome of the Mimosoideae Mimosa pudica C_LIO_LIThe nitrogen-fixing root-nodule symbiosis relies on an ancestral transcriptomic response C_LIO_LIAll symbiotic traits involve genes of the ancestral symbiotic program C_LIO_LISymbiont perception, nodule organogenesis and nitrogen-fixation are essentially ancestral processes C_LIO_LIConvergent evolution of intracellular accommodation of symbionts additionally involves lineage-specific genes C_LI

plant biology↗

bioRxiv2022

A selective bottleneck during host entry drives the evolution of new legume symbionts

During the emergence of new host-microbe symbioses, multiple selective pressures-acting at the different steps of the microbial life cycle-shape the phenotypic traits that jointly determine microbial fitness. However, the relative contribution of these different selective pressures to the adaptive trajectories of microbial symbionts are still poorly known. Here we characterized the dynamics of phenotypic adaptation and its underlying genetic bases during the experimental evolution of a plant pathogenic bacterium into a legume symbiont. We observed that fast adaptation was predominantly driven by selection acting on competitiveness for host entry, which outweighed selection acting on within-host proliferation. Whole-population sequencing of evolved bacteria revealed that phenotypic adaptation was supported by the continuous accumulation of new mutations and the sequential sweeps of cohorts of mutations with similar temporal trajectories. The identification of adaptive mutations within the fixed mutational cohorts showed that all of them improved competitiveness for host entry, while only a subset of those also improved within host proliferation. Computer simulations predict that this effect emerges from the presence of a strong selective bottleneck at host entry. Together, these results show how selective bottlenecks can alter the relative influence of selective pressures acting during bacterial adaptation to multistep infection processes.

evolutionary biology↗