Enhanced ureide partitioning improves soybean performance under drought stress

Soybean [Glycine max (L.) Merr.] fixes atmospheric nitrogen through a symbiotic relationship with rhizobia in root nodules to produce allantoin and allantoic acid. These ureides serve as primary nitrogen transport compounds that are moved from nodules to shoots in support of physiological functions and organ growth. Nodule ureide permease 1 (UPS1) is important for this transport process. Drought stress inhibits nitrogen fixation and reduces productivity in soybean, which has been associated with the accumulation of ureides in both nodule and shoot tissues. In this study, it was hypothesized that changes in ureide nodule-to-leaf-to-sink partitioning through manipulation of UPS1 function would alter ureide tissue concentrations, ultimately influencing soybean responses to drought. Soybean plants overexpressing UPS1 were exposed to moderate and severe drought conditions. Changes in organ and phloem ureide concentrations indicated enhanced nodule-to-shoot ureide transport and increased sink nitrogen supply in the transgenic plants compared with control wild-type plants. We further uncovered improvements in carbon fixation, partitioning, and availability for nitrogen fixation, resulting in increased nitrogen gains and better growth of the drought-stressed UPS1-overexpressing lines. Overall, our findings demonstrate that enhanced ureide partitioning contributes to improved soybean performance not only under well-watered conditions but also under drought stress.