Legume adaptation to sulfur deficiency

BAP SPE EA GEAPSI IPMBAPSPEEAGEAPSIIPMBecause sulfur-deficiency represents an agronomic issue for crops and notably for the quality of legume products, it is necessary to provide sulfur fertilizers according to crop sulfur needs along with improving sulfur use efficiency. To achieve this goal, increased knowledge of how plants respond to sulfur-deficiency is required. We subjected Medicago truncatula, a model legume species, to sulfur deficiency at different developmental stages and compared yield, nutrient allocation and seed traits. We revealed an impressive plasticity of M. truncatula that varied according to the S-stress period and influenced seed composition and germination. Sulfur deficiency at a mid-vegetative stage decreased yield and altered the allocation of nitrogen and carbon to seeds, leading to reduced levels of major oligosaccharides in mature seeds, which were dramatically affected in their germination. Significantly, plants deprived of sulfur at flowering adapted well by remobilizing the nutrients from source organs to seeds, ensuring adequate quantities of carbon and nitrogen in seeds. The efficient remobilization of nutrients in these plants might be explained by vacuolar sulfate efflux to maintain the metabolism of leaves and seeds throughout reproductive growth, as suggested through gene expression profiling and metabolomics. Some processes were uncovered in leaves that may help maintaining high remobilization rates to seeds in response to S-deficiency. For example, gene expression analysis of the putative vacuolar sulfate transporter SULTR4;1 in leaves revealed an up-regulation in response to sulfur-deficiency from the flowering stage, suggesting this transporter may provide sulfate to support the high demand for sulfate reduction and/or for transport to seeds. The ongoing work on the importance of vacuolar sulfate efflux in leaves using TILLING mutants for SULTR4;1 in both legume species, M. truncatula and pea, will be presented. This work was initiated through funding from the Regional Council of Burgundy and continued in the frame of the SERAPIS project coordinated by the Roullier group