Analysis of the genetic basis of symbiotic partner choice for improving symbiotic nitrogen fixation in pea – GRaSP

GRaSP (Genetics of Rhizobia Selection by Pea) is a collaborative research project that proposes an original approach to improve the pea-Rhizobium beneficial interaction by mobilizing a multidisciplinary complementary expertise of four different academic French partners together with a private partner involved in the promotion of grain legume cultivation in France. Legumes, because of their ability to form a beneficial symbiotic interaction with nitrogen-fixing Rhizobium bacteria, are projected to play an increasingly important role in sustainable agriculture. Moreover, legumes are a valuable source of protein for both feed and food, but are not grown as extensively as would be expected in France and Europe due to variability in yield and protein content. For these reasons genomic approaches are being developed to improve several important agronomic traits essential to develop higher and more stable yielding varieties in major legume crops such as pea. However, to date little attention has been paid to improving the interaction with its symbiotic partner, especially when the symbiotic partner is a mix of different Rlv strains. Establishment of the symbiosis involves mutual recognition of the plant and rhizobia partners in the soil, followed by the development of root symbiotic organs called nodules. The symbiotic interaction between pea and rhizobia is specific to strains of Rhizobium leguminosarum sv. viciae (Rlv). Past research has pointed out the role of early pea-Rlv signaling events in partner selection, but a broad understanding of the genetic determinants that govern partner choice and competitiveness for nodulation between Rlv strains in mixture is lacking. In the GRaSP project, two complementary strategies are proposed to improve this knowledge. The first one will decipher the genetic architecture of the complex trait of pea-Rlv partner choice and identify specific loci that underlie this phenotype though a Genome Wide Association Study. In parallel, the second strategy will investigate the role of variation of several pea and Rlv genes that control the specificity of symbiosis, i.e. recognition by the plant of symbiotic signals produced by rhizobia. Both approaches will benefit from large pea and Rlv collections, increasing genomic resources and high-throughput phenotyping abilities that are available among the four academic partners of the consortium. A proof-of concept of the selection for improved pea-Rhizobium associations identified in the two different approaches will be tested through the expertise of the private partner in different field conditions where data for their Rlv native population diversity are already available. GRaSP will lead to predictive understanding of pea-Rlv partner choice and knowledge-based molecular strategies which will be useful to breed peas for improved nodulation in fields with highly competitive and efficient rhizobial inocula.