Wheat decision: to respond or not respond to available nitrogen

作为绿色革命的一部分，农作物品种和农业实践的发展为20世纪的人口增长做出了贡献。然而，其中一些做法是不可持续的，因为它们对环境有害。特别是，小麦等高产谷类作物受益于通过哈伯-波什法生产的氮肥的施用，而哈伯-波什法会产生大量的温室气体。此外，农田氮素的施用和吸收是低效的过程，这导致氮在水生生态系统中逸出，造成富营养化，或在陆地生态系统中逸出，导致温室气体挥发。为了持续生产谷类作物，培育氮肥需要量低、产量高的作物品种十分重要。增加土壤中氮的可用性对产量有很强的影响，这是由每棵植物上穗/穗数量的增加所驱动的。但在氮素供应增加的情况下，单位氮素产量下降。在氮素水平增加的情况下，植物对氮有效性增加的反应，即产量的多少，会降低。在这个项目中，我们的目标是更好地了解植物对土壤中可用氮的反应，并将这种反应与它们已经获得的氮量以及它们的需求进行协调。我们将与小麦合作，因为它关系到全世界45亿人的粮食安全，也因为研究这一物种的工具已经出现。我们将重点关注独脚金内酯，因为这是一种小分子，当植物在低磷低氮条件下生长时，主要在根部产生，可以运输到茎部。它们可以调节每棵小麦植株上产生的穗数，我们的目标是测试它们的产生和感知是否对植物对氮做出反应是必要的。为此，我们将使用缺乏特定基因的小麦植物，这些基因使它们对独角麦内酯不敏感。这些实验将使我们能够产生新的知识，对特定基因的作用，已知参与感知和信号的孤角麦内酯，氮响应。我们也有兴趣了解在低氮条件下如何调节独脚金内酯的生产，以及它是否与当地外部氮的可用性或植物的氮状态有关，即植物是否在充足的氮条件下生长。氮素有效度提高的条件下，施氮对籽粒蛋白质含量也有影响。这一特性对于决定谷物的使用和价格尤其重要，谷物蛋白质含量高是制作面包所必需的，并且与谷物灌浆时植物从土壤中吸收氮的能力有关。我们已经证明，当植物生长在氮可用性增加的情况下，这种能力会降低。在这个项目中，我们将研究高氮状态如何导致花后氮吸收量降低。我们的目标是产生与植物基本认识相关的新信息，并有助于开发可以在更可持续的农业条件下种植的新作物品种。

Crop varieties and agricultural practises developed as part of the Green Revolution have contributed to feeding the population growth of the 20th century. However, some of these practises are not sustainable because they are detrimental to the environment. In particular, high yield cereal crop such as wheat have benefited from the application of nitrogen fertiliser generated through the Haber-Bosh process, which produce large amount of greenhouse gases. In addition, the application and uptake of nitrogen in the field are inefficient processes, which lead to escape of nitrogen in aquatic ecosystems causing eutrophication or in terrestrial ecosystems leading to greenhouse gases volatilisation. In order to continue producing cereal crop sustainably, it is important to grow crop varieties that can produce high yield with lower need for nitrogen application. Increasing the availability of nitrogen in the soil has a strong effect on yield, this is driven by an increase in the number of spikes/heads on each plants. However, under increased nitrogen supply, the amount of yield produced per unit of nitrogen added decreases. The plant response to increasing nitrogen availability, how much yield is produced, decreases under increasing nitrogen levels. Within this project we aim to gain a better understanding of how plants respond to nitrogen available in the soil and coordinate this response with how much they have already acquire and what is their need. We will work with wheat because it is relevant to the food security of 4.5 billion people throughout the world and because tools to study this species have become available. We will focus on strigolactone as these are small molecules produced mostly in the roots when plants are growing under low phosphorus and low nitrogen conditions, that can be transported to the shoot. These can modulate the number of spikes produced on each wheat plant and we aim to test whether their production and their perception is necessary for plant to respond to nitrogen. For this, we will use wheat plants that are lacking specific genes which render them insensitive to strigolactone. These experiments will allow us to generate new knowledge on the role of specific genes known to be involved in the perception and signalling of strigolactone, in nitrogen responsiveness. We are also interested in understanding how strigolactone production is regulated under low nitrogen conditions, and whether it is linked to the local external availability of nitrogen or the nitrogen status of the plants i.e. whether the plants have been grown under sufficient nitrogen. The dampening effect of nitrogen application under increased nitrogen availability also affect grain protein content. This trait is particularly important for determining the use and price of the grains, high grain protein content is necessary for breadmaking, and is linked to the capacity of the plant to take up nitrogen from the soil when the grains are filling. We have shown that this capacity is reduced when plants are growing under increased nitrogen availability. Within this project, we will study how high nitrogen status can also lead to lower post-anthesis nitrogen uptake. We aim to generate new information that is relevant to the fundamental understanding of plant and that is useful to develop new crop varieties which can be grown under more sustainable agricultural conditions.