Dissertation/Thesis Abstract

Understanding the physiological significance of ureide transport processes in soybean (<i>Glycine max</i> (L.) Merr.)
by Collier, Ray, Ph.D., Washington State University, 2012, 279; 3517385
Abstract (Summary)

The ureides allantoin and allantoic acid are the major long-distance forms of nitrogen (N) in nodulated tropical legumes like French bean ( Phaseolus vulgaris) and soybean (Glycine max). The ureides are synthesized in nodules and roots and are then translocated in the xylem to the shoot for transient storage, catabolism, or loading into the phloem for further distribution of N to sink tissues like developing pods. Previous research showed that French bean PvUPS1, transports allantoin in yeast. In this study two UPS1 homologs from soybean were identified and their importance for source-sink translocation of ureides and soybean physiology analyzed.

First, the putative ureide transporters GmUPS1-1 and GmUPS1-2 were isolated from soybean nodules, and their functional analysis in yeast indicated that both soybean proteins transport allantoin and allantoic acid. Analysis of the physiological function of the ureide transporters in nodules using an RNAi approach in composite soybean plants demonstrated that the GmUPS1 proteins are important for export of ureides from nodules and for shoot N supply. The results further showed that UPS1 transporter function in nodules affects N2 fixation and metabolism, probably by a feedback regulatory mechanism. Additionally, it was demonstrated that N levels in nodules regulated nodule development downstream of nodule initiation.

To understand the role of ureide transporters in shoot N partitioning, PvUPS1 from French bean was expressed in soybean under the control of the PvUPS1 promoter that targets gene expression to the phloem. Phloem ureide levels were increased in the UPS1 overexpressors, supporting that UPS1 proteins regulate phloem loading and source-sink partitioning of N. Furthermore, ureide levels in root, xylem sap, stem, and leaves were increased in the UPS1 overexpressors, suggesting that increased phloem loading positively regulates N uptake and ureide synthesis in the roots, as well as root to shoot translocation of ureides. Finally, increased phloem loading of ureides in transgenic soybean plants led to increased growth, seed protein levels, seed number, and total seed yield. Taken together, the presented research demonstrates that ureide transporter function in soybean plants is essential to N metabolism and source-sink N partitioning, and it affects plant growth and productivity.

Indexing (document details)
Advisor: Tegeder, Mechthild
Commitee: Edwards, Gerald, Knoblauch, Michael, Lange, B. Markus
School: Washington State University
Department: Molecular Plant Sciences
School Location: United States -- Washington
Source: DAI-B 73/12(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Plant biology, Plant sciences, Biochemistry
Keywords: Membrane, Noduless, Source-sink, Soybeans, Transport, Ureide
Publication Number: 3517385
ISBN: 9781267476531