CE12 - Génétique, génomique et ARN

CrossOver interference phenomenon: regulating crossover number and spatial PATTerning during meiosis – CO-PATT

The CO-PATT project combines genetics, high-throughput genetic screens, genomics, molecular biology, cytological and modelling approaches in three model organisms: the fungus S. macrospora (Partner 1), the plant A. thaliana (Partner 2) and S. cerevisiae (Partner 3) with manifest synergies. (i) S. macrospora and A. thaliana provide powerful systems for visualizing and dissecting chromosome dynamics in wild type and mutants because, contrary to S. cerevisiae and mammals, meiosis proceeds to its end even when pairing or recombination defects are present, thus facilitating complete multi-stage analysis of mutant defects. Moreover, techniques to analyze quantitatively CO patterning and chromosome-axis lengths for each single chromosome in single cells are available in both Sordaria and Arabidopsis (used for a long time in S. macrospora by Partner 1 or recently developed by Partner 2 in A. thaliana). (ii) A. thaliana and S. cerevisiae display unique powerful genetic tools together with cutting-edge genomics. (iii) All three organisms allow the modelling by Partner 4 of the interference effects. (iv) The high-throughput method developed by Partner 3 to measure recombination rates and CO interference in S. cerevisiae provides a unique opportunity to set up a genetic screen sensitive enough to detect small interference defects, which would not be possible in A. thaliana and S. macrospora. Conversely, the new components of the SUMO/STUbL pathway issued from Partner 3’s screen will be further analyzed by the more powerful cytological tools of Partners 1 and 2.

Based on these robust preliminary results, the CO-PATT project will combine multidisciplinary approaches to understand the mechanisms and players involved in CO interference by:
(1) Precisely characterize involved molecular mechanisms and the evolutionary conservation of the TopoII/Slx pathway, and study the axis/CO interference relationship in S. macrospora and Arabidopsis thaliana, using the high resolution of the single-cell imaging approaches available in these two model organisms.
(2) Find and functionally characterize new components involved in the implementation or the regulation of CO interference. For this, we will take advantage of the complementarity between our three biological systems. Mutants will be screened in S. cerevisiae using a high-throughput genetic screen with fluorescent markers and flow cytometry allows to screen for CO rates in large populations. They will be functionally analyzed not only in S. cerevisiae but also in S. macrosopora and A. thaliana to get more insights on the link between CO and axis length.
(3) Develop models and computational tools to analyse the “range” out of which Interference acts in the different recombination and/or pairing mutants characterized in the previous parts of the project.

Meiotic COs are essential to fertility, allowing correct segregation of homologous chromosomes and genomic evolution by leading to new allelic combinations that may carry advantageous traits. Our project is aiming at functional characterization of the underlying molecular mechanism that govern CO number and patterning and will have clear implication for plant breeding. Indeed, plant breeder search to create new varieties that outperform the parents by combining their valuable traits. However, the fact that CO number (low number per meiosis) and localization (existence of hypo-recombinogenic regions interspaced by hyper-recombinogenic regions and the CO interference phenomenon that disfavour close CO formation) are strictly controlled can thwart breeder’s efforts to construct the desired combinations of alleles. Therefore, the characterization of key players and mechanism involved in CO patterning regulation have the potential to harness the portion of genetic diversity that remains inaccessible to breeders and to contribute to accelerate genetic gains and new varieties generation. Technologies aiming at controlling CO formation are currently few. However, with the necessity to increase crop production to meet the population increase and counteract the putative global warming impact on crop productivity, economic and societal challenges are high.

Revues à comité de lecture :
C. Girard , K. Budin , S. Boisnard , L. Zhang , R. Debuchy , D. Zickler , E. Espagne . RNAi-Related Dicer and Argonaute Proteins Play Critical Roles for Meiocyte Formation, Chromosome-Axes Lengths and Crossover Patterning in the Fungus Sordaria macrospora. Front Cell Dev Biol. 2021 Jun 28;9:684108.

Communications (conférence) :

1. Determinants of meiotic crossover number and distribution: a role for RNAi factors in Sordaria macrospora. Stéphanie Boisnard, Karine Budin, Robert Debuchy, Eric Espagne, Liangran Zhang, Denise Zickler, and Chloe Girard (Talks)

2. SCEP1 and SCEP2 are two novel components of the Syntonemal Complex in Arabidopsis thaliana.Nathalie Vrielynck, Marion Peuch, Aurélie Chambon, Raphaël Guerois*, Mathilde Grelon and Christine Mézard Gordon Research Conference on meiosis. Colby Sawyer College. June 5 - 10, 2022 (Poster)

Submission summary

Shuffling of maternal and paternal alleles through meiotic recombination increases genetic diversity in the progeny and ensures the accurate segregation of homologous chromosomes during the first meiotic division. Errors in segregation lead to the formation of aneuploid gametes and/or sterility. However, the mechanisms responsible for both formation and regulation of COs remain largely unknown.
Meiotic recombination starts with the formation of programmed DNA double strand breaks (DSBs). Their accurate repair is essential for both the pairing of homologous chromosomes and the establishment of the pairing structure called the synaptonemal complex (SC). The repair of DSBs preferentially uses the homologous chromosome as a template, generating COs and non-crossing-overs (NCOs). The formation of both DSBs and COs is tightly regulated. The choice between NCO and CO is crucial to ensure the presence of at least one CO per homologous pair, independently of the size of the chromosomes. In addition, the occurrence of a CO at one position disfavors the occurrence of a CO nearby, leading to evenly spaced COs along the chromosomes by the phenomenon of interference. As this phenomenon requires the propagation of an inhibition signal along the chromosome, the number of COs per bivalent depends, therefore, on both the length of the axis and the strength of the interference signal.
Although CO interference was first described in 1916, the actors of this essential regulatory process remain unknown. The only pathway known to play a role in interference modulation is the TopoII/Slx pathway, involved in the posttranslational modifications (SUMOylation and ubiquitination) of two axis components in Saccharomyces cerevisiae (TopoII, Red1). Preliminary results showed that this pathway is conserved in Sordaria macrospora with moreover, in the null mutants of this pathway, a correlation between the increased number of COs and changes in chromosome axis lengths, when compared to wild type.
Based on these robust preliminary results, the CO-PATT project will combine multidisciplinary approaches to understand the mechanisms and players involved in CO interference by:
(1) Precisely characterize involved molecular mechanisms and the evolutionary conservation of the TopoII/Slx pathway, and study the axis/CO interference relationship in S. macrospora and Arabidopsis thaliana, using the high resolution of the single-cell imaging approaches available in these two model organisms.
(2) Find and functionally characterize new components involved in the implementation or the regulation of CO interference. For this, we will take advantage of the complementarity between our three biological systems. Mutants will be screened in S. cerevisiae using a high-throughput genetic screen with fluorescent markers and flow cytometry allows to screen for CO rates in large populations. They will be functionally analyzed not only in S. cerevisiae but also in S. macrosopora and A. thaliana to get more insights on the link between CO and axis length.
(3) Develop models and computational tools to analyse the “range” out of which Interference acts in the different recombination and/or pairing mutants characterized in the previous parts of the project.
By shedding a new light on the molecular mechanisms that govern CO number and patterning along chromosomes, the CO-PATT project will bring important knowledge to the scientific communities working either on fertility or plant breeding

Project coordination

Eric Espagne (Institut de Biologie Intégrative de la Cellule)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IJPB INRAE Institut Jean-Pierre BOURGIN
I2BC Institut de Biologie Intégrative de la Cellule
GQE Génétique quantitative et Evolution - Le Moulon
IPS2 Institut des Sciences des Plantes de Paris Saclay

Help of the ANR 582,008 euros
Beginning and duration of the scientific project: December 2020 - 48 Months

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