Modelling Sex-Specific Crossover Patterning in Arabidopsis

International audience"Interference" is a major force governing the patterning of meiotic crossovers. A leading model describing how interference influences crossover patterning is the beam-film model, a mechanical model based on the accumulation and redistribution of crossover-promoting “stress” along the chromosome axis. We use the beam-film model in conjunction with a large Arabidopsis reciprocal backcross data set to gain “mechanistic” insights into the differences between male and female meiosis, and crossover patterning. Beam-film modeling suggests that the underlying mechanics of crossover patterning and interference are identical in the two sexes, with the large difference in recombination rates and distributions able to be entirely explained by the shorter chromosome axes in females. The modeling supports previous indications that fewer crossovers occur via the class II pathway in female meiosis and that this could be explained by reduced DNA double-strand breaks in female meiosis, paralleling the observed reduction in synaptonemal complex length between the two sexes. We also demonstrate that changes in the strength of suppression of neighboring class I crossovers can have opposite effects on "effective" interference depending on the distance between two genetic intervals

Reducing MSH4 copy number prevents meiotic crossovers between non-homologous chromosomes in Brassica napus

In allopolyploids, correct chromosome segregation requires suppression of non-homologous crossovers while levels of homologous crossovers are ensured. To date, no mechanism able to specifically inhibit non-homologous crossovers has been described in allopolyploids other than in bread wheat. Here, we show that reducing the number of functional copies of MSH4, an essential gene for the main crossover pathway, prevents non-homologous crossovers in allotetraploid Brassica napus. We show that non-homologous crossovers originate almost exclusively from the MSH4-dependent recombination pathway and that their numbers decrease when MSH4 returns to single copy in B. napus; by contrast, homologous crossovers remain unaffected by MSH4 duplicate loss. We also demonstrate that MSH4 systematically returns to single copy following numerous independent polyploidy events, a pattern that is probably not by chance. These results suggest that stabilization of allopolyploid meiosis can be enhanced by loss of a key meiotic recombination gene

Mutations in AtPS1 (Arabidopsis thaliana Parallel Spindle 1) Lead to the Production of Diploid Pollen Grains

Polyploidy has had a considerable impact on the evolution of many eukaryotes, especially angiosperms. Indeed, most—if not all—angiosperms have experienced at least one round of polyploidy during the course of their evolution, and many important crop plants are current polyploids. The occurrence of 2n gametes (diplogametes) in diploid populations is widely recognised as the major source of polyploid formation. However, limited information is available on the genetic control of diplogamete production. Here, we describe the isolation and characterisation of the first gene, AtPS1 (Arabidopsis thaliana Parallel Spindle 1), implicated in the formation of a high frequency of diplogametes in plants. Atps1 mutants produce diploid male spores, diploid pollen grains, and spontaneous triploid plants in the next generation. Female meiosis is not affected in the mutant. We demonstrated that abnormal spindle orientation at male meiosis II leads to diplogamete formation. Most of the parent's heterozygosity is therefore conserved in the Atps1 diploid gametes, which is a key issue for plant breeding. The AtPS1 protein is conserved throughout the plant kingdom and carries domains suggestive of a regulatory function. The isolation of a gene involved in diplogamete production opens the way for new strategies in plant breeding programmes and progress in evolutionary studies

Book review: Polyploidy and genome evolution. Pamela S. Soltis, Douglas E. Soltis. eds. Springer

Book review: Polyploidy and genome evolution. Pamela S. Soltis, Douglas E. Soltis. eds. Springe

Manipulation of crossover frequency and distribution for plant breeding

The crossovers (COs) that occur during meiotic recombination lead to genetic diversity upon which natural and artificial selection can act. The potential of tinkering with the mechanisms of meiotic recombination to increase the amount of genetic diversity accessible for breeders has been under the research spotlight for years. A wide variety of approaches have been proposed to increase CO frequency, alter CO distribution and induce COs between non-homologous chromosomal regions. For most of these approaches, translational biology will be crucial for demonstrating how these strategies can be of practical use in plant breeding. In this review, we describe how tinkering with meiotic recombination could benefit plant breeding and give concrete examples of how these strategies could be implemented into breeding programs

Homoeologous exchanges in allopolyploids: how Brassica napus established self‐control!

International audienc

Focus on polyploidy

Polyploidy (whole-genome duplication) has played a pervasive role in the evolution of fungi and animals, and is particularly prominent in plants (Wendel & Doyle, 2005; Cui et al., 2006; Otto, 2007; Wood et al., 2009). This important evolutionary phenomenon has attracted renewed and growing interest from the scientific community in the last decade since it was discovered that even the smallest plant genomes considered to be ‘diploid' (e.g. Arabidopsis thaliana, reviewed in Henry et al., 2006) have incurred at least one round of whole-genome duplication, possibly predating the origins of the angiosperms (Soltis et al., 2009). Polyploidy is an important speciation mechanism for all eukaryotes and has profound impacts on biodiversity dynamics and ecosystem functioning. Newly formed polyploids, and particularly those of hybrid origin (allopolyploids), frequently exhibit rapid range expansion (Ainouche et al., 2009), and over long periods of evolutionary time, polyploidy has increased morphological complexity and probably reduced the risk of species extinction (Fawcett et al., 2009). Last, but not least, genome duplication has often provided the raw material for plant domestication (e.g. wheat, Dubkovsky & Dvorak, 2007) and thus has had a major impact on human societies and the development of an agrarian lifestyle

Une autre vision de la sélection variétale

National audienceLes derniers acquis de la recherche sur les mécanismes de la recombinaison génétique, lors de la méiose, ouvrent de nouvelles voies de sélection des caractères d’intérêts chez les plantes cultivées

Differentiation between natural and cultivated populations of Medicago sativa (Leguminosae) from Spain: analysis with random amplified polymorphic DNA (RAPD) markers and comparison to allozymes

International audienc