Olivier Coriton | PubMed Health

PubMed2026

Nissolia brasiliensis as a nonnodulating model legume.

The nitrogen-fixing root nodule symbiosis is specifically formed by 4 orders of angiosperms. The largest of these 4 orders includes the legume family, the Fabaceae. Among legumes, historical model species have emerged, such as the root nodule symbiosis-forming Medicago truncatula and Lotus japonicus or, more recently, Aeschynomene evenia. By contrast, legume species that have lost root nodule symbiosis have been largely ignored. Here, we describe the first near chromosome-level assembly for a non-root nodule symbiosis-forming legume, the tropical Papilionoideae Nissolia brasiliensis. We compared its genome to closely related legumes and identified genes associated with root nodule symbiosis. Finally, we developed a stable transformation protocol that can be deployed in the future to reevolve root nodule symbiosis in legumes, a first step toward the goal of engineering root nodule symbiosis in nonlegume crops.

Fabaceae↗

PubMed2025

Genomic Divergence Shaped the Genetic Regulation of Meiotic Homologous Recombination in Brassica Allopolyploids.

The tight regulation of meiotic recombination between homologs is disrupted in Brassica AAC allotriploids, a genomic configuration that may have facilitated the formation of rapeseed (Brassica napus L.) ∼7,500 years ago. Indeed, the presence of the haploid C genome induces supernumerary crossovers between homologous A chromosomes with dramatically reshaped distribution. However, the genetic mechanisms driving this phenomenon and their divergence between nascent and established lineages remain unclear. To address these concerns, we generated hybrids carrying additional C chromosomes derived either from an established lineage of the allotetraploid B. napus or from its diploid progenitor B. oleracea. We then assessed recombination variation across twelve populations by mapping male meiotic crossovers using single nucleotide polymorphism markers evenly distributed across the sequenced A genome. Our findings reveal that the C09 chromosome of B. oleracea is responsible for the formation of additional crossovers near pericentromeric regions. Interestingly, its counterpart from an established lineage of B. napus shows no significant effect on its own, despite having a similar content of meiotic genes. However, we showed that the B. napus C09 chromosome influences crossover formation through inter-chromosomal epistatic interactions with other specific C chromosomes. These results provide new insights into the genetic regulation of homologous recombination in Brassica and emphasize the role of genomic divergence since the formation of the allopolyploid B. napus.

Meiosis↗