Integrating Photoassimilate Source to Sink Transport in Legumes to Enhance Seed Development and Nutrition

Washington State University, Pullman WA

Investigators

Abstract

Non-technical Summary: The development of strategies to improve crop productivity to meet growing societal needs for food supply and alternative sources of energy provides a challenge to current and future research on plants. In addition, the balanced intake of essential nutrients or metabolites is important for human nutrition worldwide, but their content is often sub-optimal in crop species, as is the case for the essential amino acid methionine in legume seeds. In higher plants, carbon and nitrogen are quantitatively the most important nutrients for plant development. The macronutrients are taken up by the plant and are assimilated into sucrose and amino acids. These are then transported in the vascular system to the seeds to support growth and accumulation of storage reserves such as proteins, starch, or oils. The goal of this project is to understand and manipulate carbon and nitrogen assimilate transport to legume seeds, and to overcome potential bottlenecks of assimilate movement. This study will provide clues as to how transporter proteins function in delivery of carbon and nitrogen nutrients to seeds, and on their critical role in seed yield and nutritional quality. Technical Description of the Project: Transgenic modifications of amino acid and sucrose transporters have underlined their essential roles in assimilate partitioning; however, there has been only limited success integrating transporter function with seed development, seed metabolism, and the synthesis of seed storage compounds and their nutritional quality. Current data suggest that a bottleneck within the long distance transport pathway lies in the transporter activity, or the lack of it, in both leaves (i.e. phloem) and embryos. Furthermore, research supports strong regulatory control by nitrogen assimilate transporters over metabolic processes up and downstream of their function. In this study, Pisum sativum L. (pea) will be used as a model system. Transgenic plants will be analyzed, in which photoassimilate transporters are simultaneously overexpressed in the phloem and in cotyledon transfer cells, where assimilate import into the embryo occurs. Potential constraints will be overcome in source to sink transport of photoassimilates to promote sink development and seed storage product accumulation (Aim 1) and to resolve if and how different embryo uptake systems affect seed assimilate flux, metabolism and metabolite compartmentation (Aim 2). Molecular, biochemical, and cell-biological analyses, and physiological techniques, as well as a combination of magnetic resonance imaging (MRI) for assimilate flux studies in living seeds and modeling approaches will be used to answer some long-standing questions about rate limiting and regulatory processes in assimilate transfer to, and distribution and usage within, the main embryo storage sites. The proposed activities will further promote student and public education in plant biology by discussing research schemes in the classroom, by mentoring and training undergraduate and graduate students in research, by engaging students in international collaborations, and through demonstrations and activities involving the local community. Overall, this project will foster effective integration of plant biology education and research.