S03 - Session O1 - Natural genetic diversity of barrel medic provides insight into the physiological bases of legume early seedling performance and plasticity to nitrate

Authors: Douae Ben Hdech, Catherine Aubry, Françoise Montrichard, Bénédicte Alibert, Daniel Beucher, Guillaume Tcherkez, Anis M Limami, Béatrice Teulat *

Early developmental stages are particularly challenging for seedling, especially under limited nitrogen (N) input. Finding physiologically/metabolically N-efficient lines is thus critical including in Legumes where nitrate uptake and assimilation occur before nodulation. Here, we took advantage of barrel Medic ( Medicago truncatula ) natural diversity (192 accessions) to identify markers of seedling performance with or without nitrate supply. Traits associated with organ elongation and seed biomass remobilisation were determined during seedling heterotrophic growth, and indices of plasticity to the absence of nitrate were calculated. Seedling growth response traits allowed us to group accessions into four categories corresponding to four nitrate response physiotypes. The GWAS (Genome-Wide Association Study) analysis allowed identifying chromosomal regions associated with performance and plasticity traits. In particular, two regions containing genes encoding sugar transporters and glutathione S-transferases (GSTs) were associated with the response of seedling elongation to nitrate. This suggests that the ability to maintain growth in the absence of mineral N source appears to be related to sugar movement and to sulfur (S) redox metabolism. An in silico analysis of GST gene sequences as well as the monitoring of GST activity during seedling heterotrophic growth completed the study. Taken as a whole, our findings suggest an interaction between GSTs, reactive oxygen species (ROS) and nitrate to control cell elongation during heterotrophic growth, and that N/S/ROS metabolism seems to be a key player for the fitness of genotypes in response to nitrate availability.