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

非技术总结：制定提高作物生产力的策略，以满足日益增长的社会对粮食供应和替代能源的需求，对当前和未来的植物研究提出了挑战。此外，均衡摄入必需营养素或代谢物对全世界的人类营养都很重要，但它们的含量在作物物种中往往不是最佳的，就像豆科植物种子中必需氨基酸蛋氨酸的情况一样。在高等植物中，碳和氮在数量上是植物发育最重要的营养物质。大量营养素被植物吸收并被同化成蔗糖和氨基酸。然后，这些物质通过维管系统输送到种子中，以支持种子的生长和储存储备的积累，如蛋白质、淀粉或油脂。本项目的目标是了解和控制碳和氮同化物向豆科植物种子的运输，并克服同化物运动的潜在瓶颈。这项研究将为了解转运蛋白如何将碳和氮营养物质输送到种子，以及它们在种子产量和营养品质中的关键作用提供线索。项目技术描述：氨基酸和蔗糖转运体的转基因修饰强调了它们在同化物分配中的重要作用；然而，将转运蛋白的功能与种子发育、种子代谢、种子储存化合物的合成及其营养品质结合起来的研究成果有限。目前的数据表明，长距离运输途径的瓶颈在于叶片（即韧皮部）和胚胎中的转运蛋白活性或缺乏转运蛋白。此外，研究支持氮同化转运体对其功能上下游代谢过程的强大调节控制。本研究以豌豆（Pisum sativum L.）为模型系统。将分析转基因植物，其中光同化转运蛋白同时在韧皮部和子叶转移细胞中过度表达，在那里同化物质进入胚胎发生。将克服光同化物从源到库运输的潜在限制，以促进库发育和种子储存产物积累（目标1），并解决不同的胚胎吸收系统是否以及如何影响种子同化物通量、代谢和代谢物区隔（目标2）。分子、生物化学、细胞生物学分析和生理学技术，以及结合磁共振成像（MRI）对活种子中同化物通量的研究和建模方法，将用于回答一些长期存在的问题，即同化物转移到主要胚胎储存部位的速率限制和调节过程，以及在主要胚胎储存部位的分布和使用。拟议的活动将通过在课堂上讨论研究计划、指导和培训本科生和研究生的研究、让学生参与国际合作以及通过让当地社区参与示范和活动，进一步促进学生和公众对植物生物学的教育。总的来说，这个项目将促进植物生物学教育和研究的有效整合。

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.