Biology subjects

Mafessoni, F.

Publications and source records attributed to Mafessoni, F..

10 recordsLinked to original sources

bioRxiv2024

A multi-omics approach to identify deleterious mutations in plants

Crops lose genetic variation due to strong founder effects during domestication, accumulating and potentially exposing recessive deleterious alleles. Therefore, identifying those deleterious variants in domesticated varieties and their functional orthologs in wild relatives is key for plant breeding, food security and in rescuing the biodiversity of cultivated crops. We explored a machine learning strategy to estimate the impact of new and existing mutations in plant genomes, leveraging multi-omics data, encompassing genomic, epigenomic and transcriptomic information. Specifically, we applied a support-vector-machine framework, previously applied to animal datasets, to published omics data of two important crops of the genus Solanum - tomato and potato - and for the model plant Arabidopsis thaliana. We show that our approach provides biologically plausible inferences on the role of mutations occurring in different genomic regions and predictions that correlate with natural genetic variation for the three species, supporting the validity of our estimates. Finally, we show that our estimates outperform existing methods relying exclusively on phylogenetic conservation and not leveraging the availability of omics data for crop species. This approach provides a simple score for researchers to prioritize variants for gene editing and breeding purposes.

bioinformatics↗

bioRxiv2023

A CRISPR-induced DNA break can trigger crossover, chromosomal loss and chromothripsis-like rearrangements

The fate of DNA double-strand breaks (DSBs) generated by the Cas9 nuclease has been thoroughly studied. Repair via non-homologous end-joining (NHEJ) or homologous recombination (HR) is the common outcome. However, little is known about unrepaired DSBs and the type of damage they can trigger in plants. In this work, we designed a new assay that detects loss of heterozygosity (LOH) in somatic cells, enabling the study of a broad range of DSB-induced genomic events. The system relies on a mapped phenotypic marker which produces a light purple color (Betalain pigment) in all plant tissues. Plants with sectors lacking the Betalain marker upon DSB induction between the marker and the centromere were tested for LOH events. Using this assay we detected a flower with a twin yellow and dark purple sector, corresponding to a germinally transmitted somatic crossover event. We also identified instances of small deletions of genomic regions spanning the T-DNA and whole chromosome loss. In addition, we show that major chromosomal rearrangements including loss of large fragments, inversions, and translocations were clearly associated with the CRISPR-induced DSB. Detailed characterization of complex rearrangements by whole genome sequencing, molecular, and cytological analyses, supports a model in which breakage-fusion-bridge cycle followed by chromothripsis-like rearrangements had been induced. Our LOH assay provides a new tool for precise breeding via targeted crossover detection. It also uncovers CRISPR mediated chromothripsis-lke events that had not been previously identified in plants.

genetics↗

bioRxiv2023

Uncovering the Dynamics of Precise Repair at CRISPR/Cas9-induced Double-Strand Breaks

CRISPR/Cas9-mediated genome editing relies on error-prone repair of targeted DNA double-strand breaks (DSBs). Understanding CRISPR/Cas9-mediated DSB induction and subsequent repair dynamics requires measuring the rate of cutting and that of precise repair, a hidden-variable of the repair machinery. Here, we present a molecular and computational toolkit for multiplexed quantification of DSB intermediates and repairproducts by single-molecule sequencing. Using this approach, we characterized the dynamics of DSB induction, processing and repair at endogenous loci along a 72-hour time-course in tomato protoplasts. Combining this data with kinetic modeling reveals that indel accumulation is not an accurate reflection of DSB induction efficiency due to prominent precise re-ligation, accounting for 40-70% of all repair events. Altogether, this system exposes previously unseen flux in the DSB repair process, decoupling induction and repair dynamics, and suggesting an essential role of high-fidelity repair in limiting CRISPR editing efficiency in somatic cells.

molecular biology↗

bioRxiv2022

The genetic structure of a wild wheat population has remained associated with microhabitats over 36 years

Long-term genetic studies of wild populations are very scarce, but are essential for connecting ecological and population genetics models, and for understanding the dynamics of biodiversity. We present a study of a wild wheat population sampled over a 36-year period at high spatial resolution. We genotyped 832 individuals from regular sampling along transects during the course of the experiment. Genotypes were clustered into ecological microhabitats over scales of tens of metres, and this clustering was remarkably stable over the 36 generations of the study. Simulations show that it is difficult to explain this spatial and temporal stability using only limited dispersal, suggesting a role for fine-scale local adaptation to ecological parameters. Using a common-garden experiment, we showed that the genotypes found in distinct microhabitats differ phenotypically, further supporting the hypothesis of local adaptation. Our results provide a rare insight into the population genetics of a natural population over a long monitoring period.

evolutionary biology↗

bioRxiv2021

Non-genetic maternal effects shape individual differences in cortisol phenotypes in wild chimpanzees

Glucocorticoids, such as cortisol, mediate homeostatic processes, allowing individuals to adjust to fluctuating environments. The regulation of circadian cortisol responses, a key homeostatic function, has been shown to be heritable. However, to understand better the role of parental care in shaping physiological functioning in long-lived mammals with protracted parental care, there is a need to disentangle genetic and non-genetic parental contributions to variation in glucocorticoid phenotypes. We used a dataset of 6,123 cortisol measures from urine samples from 170 wild chimpanzees spanning 18 years of data collection. We found consistent inter-individual differences in circadian cortisol phenotypes, with differences most apparent when considering average cortisol levels given the effect of time of day. Maternal effects explained around 10% (2-18%) variation in these average cortisol levels, while variation attributable to genetic factors was not distinguishable from zero. Our results indicate, relative to genetic effects, a qualitatively stronger influence of mothers, whether via epigenetic processes or via behavioral priming for coping with stressors, in shaping cortisol phenotypes in this species. This provides novel insight into the vital role of mothers in the developmental plasticity of long-lived mammals and, more generally, the selective pressures shaping physiological plasticity.

zoology↗

bioRxiv2021

Genome sequences of the five Sitopsis species of Aegilops and the origin of polyploid wheat B-subgenome

Bread wheat (Triticum aestivum L., BBAADD) is a major staple food crop worldwide. The diploid progenitors of the A- and D-subgenomes have been unequivocally identified, that of B however remains ambiguous and controversial but is suspected to be related to species of Aegilops, section Sitopsis. Here, we report the assembly of chromosome-level genome sequences of all five Sitopsis species, namely Ae. bicornis, Ae. longissima, Ae. searsii, Ae. sharonensis, and Ae. speltoides, as well as partial assembly of Ae. mutica genome for phylogenetic analysis. Our results support that the donor of bread wheat B-subgenome is a distinct, probably extinct, diploid species that diverged from an ancestral progenitor of the B-lineage similar to Ae. mutica and Ae. speltoides. The five Sitopsis species have variable genome sizes (4.11-5.89 Gb) with high proportions of repetitive sequences (85.99-89.81%); nonetheless, they retain high collinearity with other wheat genomes. Differences in genome size are primarily due to independent post-speciation amplification of transposons rather than to inter-specific genetic introgression. We also identified a set of Sitopsis genes pertinent to important agronomic traits that can be harnessed for wheat breeding. These resources provide a new roadmap for evolutionary and genetic studies of the wheat group. SignificanceThe origin of the B-subgenome of hexaploid bread wheat remains unknown. Here we report the assembly of chromosome-level genome sequences of all five Sitopsis species of the genus Aegilops, which are previously considered as possible direct progenitors or contributors to the B-subgenome. Our comparative genomic analyses reveal that the B-subgenome originated from an unknown, most likely extinct species phylogenetically distinct from Ae. speltoides, its extant closest relative. We also provide evidence that Ae. speltoides is neither the direct progenitor of the G-subgenome of tetraploid wheat Triticum timopheevii. The high-quality Sitopsis genomes provide novel avenues to identify new important genes for wheat breeding.

evolutionary biology↗

bioRxiv2020

Unveiling diffusion pattern and structural impact of the most invasive SARS-CoV-2 spike mutation

Starting in Wuhan, China, SARS-CoV-2 epidemics quickly propagated worldwide in less than three months, geographically sorting genomic variants in newly established propagules of infections. Stochasticity in transmission within and between countries and/or actual advantage in virus transmissibility could explain the high frequency reached by some genomic variants during the course of the outbreak. Using a suite of statistical, population genetics, and theoretical approaches, we show that the globally most represented spike protein variant (i.e., the G clade, A [->] G nucleotide change at genomic position 23,403; D [->] G amino acid change at spike protein position 614) i) underwent a significant demographic expansion in most countries not explained by stochastic effects or enhanced pathogenicity; ii) affects the spike S1/S2 furin-like site increasing its conformational plasticity (short range effect), and iii) modifies the internal motion of the receptor-binding domain affecting its cross-connection with other functional domains (long-range effect). Our study unambiguously links the spread of the G614 with a non-random process, and we hypothesize that this process is related to the selective advantage produced by a specific structural modification of the spike protein. We conclude that the different conformation of the S1/S2 proteolytic site is at the basis of the higher transmission rate of this invasive SARS-CoV-2 variant, and provide structural information to guide the design of selective and efficient drugs.

evolutionary biology↗

bioRxiv2020

On the fitness of informative cues in complex environments

To be able to deal with uncertainty is of primary importance to most living organisms. When cues provide information about the state of the environment, organisms can use them to respond flexibly. Life forms have evolved complex adaptations and sensory mechanisms to use these environmental cues and extract valuable information about the environment. Previous work has shown a theoretical limit to the amount of fitness benefit possible to be extracted from the cues. We show that the previously used information theoretical approaches can be generalised to scenarios involving any potential relationship between the number of possible phenotypes and environmental states. Such cases are relevant when physiological constraints or complex ecological scenarios lead to the number of environmental states exceeding potential phenotypes. We illustrate cases in which these scenarios can emerge: along environmental gradients, such as geographical transects or complex environments, where organisms adopt different bet-hedging strategies, switching stochastically between phenotypes or developing intermediate ones. In conclusion, we develop an information-theoretic extensible approach for investigating and quantifying fitness in ecological studies.

evolutionary biology↗

bioRxiv2020

A high-coverage Neandertal genome from Chagyrskaya Cave

We sequenced the genome of a Neandertal from Chagyrskaya Cave in the Altai Mountains, Russia, to 27-fold genomic coverage. We estimate that this individual lived ~80,000 years ago and was more closely related to Neandertals in western Eurasia (1,2) than to Neandertals who lived earlier in Denisova Cave (3), which is located about 100 km away. About 12.9% of the Chagyrskaya genome is spanned by homozygous regions that are between 2.5 and 10 centiMorgans (cM) long. This is consistent with that Siberian Neandertals lived in relatively isolated populations of less than 60 individuals. In contrast, a Neandertal from Europe, a Denisovan from the Altai Mountains and ancient modern humans seem to have lived in populations of larger sizes. The availability of three Neandertal genomes of high quality allows a first view of genetic features that were unique to Neandertals and that are likely to have been at high frequency among them. We find that genes highly expressed in the striatum in the basal ganglia of the brain carry more amino acid-changing substitutions than genes expressed elsewhere in the brain, suggesting that the striatum may have evolved unique functions in Neandertals.

genomics↗

bioRxiv2017

Inter-Chromosomal Linkage Reveals Errors in the 1000 Genomes Dataset

It is often unavoidable to combine data from different sequencing centers or sequencing platforms when compiling datasets with a large number of individuals. However, the different data are likely to contain specific systematic errors that will appear as SNPs. Here, we devise a method to detect systematic errors in combined datasets. To measure quality differences between individual genomes, we study pairs of variants that reside on different chromosomes and co-occur in individuals. The abundance of these pairs of variants in different genomes is then used to detect systematic errors due to batch effects. Applying our method to the 1000 Genomes dataset, we find that coding regions are enriched for errors, where about 1% of the higher-frequency variants are predicted to be erroneous, whereas errors outside of coding regions are much rarer (<0.001%). As expected, predicted errors are less often found than other variants in a dataset that was generated with a different sequencing technology, indicating that many of the candidates are indeed errors. However, predicted 1000 Genomes errors are also found in other large datasets; our observation is thus not specific to the 1000 Genomes dataset. Our results show that batch effects can be turned into a virtue by using the resulting variation in large scale datasets to detect systematic errors.

genomics↗