THE ROLE OF NITROGEN TRANSPORT PROCESSES IN SOYBEAN [GLYCINE MAX (L.) MERR.] PHYSIOLOGY AND STRESS RESPONSE

Legumes develop a symbiotic relationship with rhizobial bacteria that reside in root nodules and fix atmospheric di-nitrogen (N2 ). In soybean [Glycine max (L.) Merr.] nodules, the fixed nitrogen (N) is used to produce the ureides allantoin and allantoic acid that serve as the primary forms of N transported from nodules to shoot tissues. Cellular import and long-distance transport of ureides is facilitated by plasma membrane-localized ureide permeases 1 (UPS1). Recent research has shown that the overexpression of UPS1 (UPS1-OE) in cortex and endodermal cells of soybean nodules led to increased nodule export of ureides and their enhanced partitioning in the xylem to the shoot, finally resulting in improved seed development. The current work demonstrates that ureide partitioning processes are equally important for the performance of non-fixing, non-nodulated soybean plants that primarily use amino acids as main N transport forms. Non-fixing soybean plants overexpressing UPS1 in the leaf phloem displayed enhanced phloem loading of ureides and sink N supply. The changes in ureide partitioning positively affected amino acid homeostasis and transport, photosynthesis, and sucrose phloem transport, leading to improved vegetative growth and higher seed yields in UPS1-OE plants compared to the wild-type control. Overall, these findings support that ureide transport processes in non-fixing soybean plants exert regulatory control over N and carbon acquisition, assimilation, and source-to-sink translocation affecting soybean productivity.