14 ERA-CAPS_Simultaneous manipulation of source and sink metabolism for improved crop yield

不同植物组织的代谢网络的能力是作物产量的关键决定因素。特别重要的是同化环境碳（CO2）和氮（NO3）的能力，将所得糖和氨基酸运输到库组织（如块茎、果实和种子）的能力，以及库组织将进入的糖和氨基酸转化为储存化合物的能力。人们对通过基因工程提高这些代谢和运输过程的能力或效率非常感兴趣。目前在这一领域工作的许多研究联盟都集中在源组织中负责碳和氮同化的初始过程。然而，很明显，无论是在理论上的理由和实验证据，整个植物的碳和氮通量的源和库组织的代谢能力共同限制。当源容量增加时，情况尤其如此：控制将不可避免地转移到库组织，库组织的代谢将严重限制工程作物的产量潜力。在本项目中，我们将在植物中实施前所未有的代谢工程策略。我们不仅将工程源和汇组织，但我们将针对多个代谢和运输过程中的每一个，试图从整个代谢网络消除流量瓶颈。该项目将利用生物射弹组合共转化的新技术，该技术允许将无限数量的转基因稳定整合到任何适合核基因组生物射弹转化的植物中的单个位点中。基于先前的知识，我们已经确定了18个将被引入番茄植物的转基因靶标。我们将产生一个多达200个转基因品系的大型文库，并将对这些品系进行果实产量筛选，与引入少量仅修饰源或库的转基因相比，期望实现产量的逐步变化。此外，该项目还将开展广泛的研究，以确定其他代谢瓶颈（通过比较代谢网络通量和酶活性），确定参与果实氮分配的转运蛋白，并确定收获指数和果实氮含量的强遗传等位基因（基于对番茄渐渗群体的分析）。这项研究将提供额外的目标，这些目标将被超级转化为表现最好的转基因品系，以评估进一步提高产量的范围。

The capacity of the metabolic networks of different plant tissues is a key determinant of the yield of crop plants. Of particular importance is the capacity to assimilate environmental carbon (CO2) and nitrogen (NO3), the capacity to transport the resultant sugars and amino acids to the sink tissues (such as tubers, fruits and seeds) and the capacity of the sink tissues to convert the incoming sugars and amino acids into storage compounds. There is a great deal of interest in increasing the capacity or efficiency of these metabolic and transport processes by genetic engineering. Many of the current research consortia working in this area are focussing on the initial processes responsible for carbon and nitrogen assimilation in the source tissues. However, it is clear both on theoretical grounds and from experimental evidence that whole plant fluxes of carbon and nitrogen are co-limited by the metabolic capacities of both source and sink tissues. This is especially true if the source capacity is increased: control will inevitably shift to the sink tissues, the metabolism of which will therefore severely limit the yield potential of an engineered crop.In this project, we will implement a metabolic engineering strategy of unprecedented scale in plants. Not only will we engineer both source and sink tissues, but we will target multiple metabolic and transport processes in each in an attempt to remove flux bottlenecks from across the metabolic network. The project will exploit the new technique of biolistic combinatorial co-transformation which allows the stable integration of an unlimited number of transgenes into a single locus in any plant amenable to biolistic transformation of the nuclear genome. Based on prior knowledge, we have identified 18 transgene targets which will be introduced into tomato plants. We will generate a large library of up to 200 transgenic lines and these will be screened for fruit yield, with the expectation of achieving a step-change in yield in comparison to the introduction of small numbers of transgenes modifying just source or sink. In addition, the project will undertake extensive research to identify additional metabolic bottlenecks (by comparison of metabolic network fluxes and enzyme activities), to identify transporters involved in fruit nitrogen allocationand to identify strong genetic alleles for harvest index and fruit nitrogen content (based on analysis of tomato introgression populations). This research will provide additional targets which will be super-transformed into the best performing transgenic line to assess the scope for even further yield increases.