Connecting grain yield and viability with photosynthetic electron transport in developing seeds

谷物作物产量的增加对人类至关重要，而该提案解决了影响粮食产量和生存能力的因素。光合电子传递（PET）提供了将碳固定在叶片中的能量，并将其运输以支持籽粒灌浆。谷类花器官也是绿色的，而PET在种子发育过程中对产量和生存能力尤为重要，但人们对其了解甚少。我们已经开发了技术和遗传工具来帮助填补这一知识空白。为什么是大麦种子？在20世纪50年代和60年代，“绿色革命”通过开发高产谷物品种，使数百万人免于饥饿，这些品种在将叶片光合作用转化为发育中的种子方面非常有效。谷物花穗的光合作用过程对高产也很重要，特别是绿色组织在谷物种子发育中的作用仍然知之甚少。对此进行调查可以为育种计划提供信息，从而进一步提高粮食产量。研究大麦是提高谷物产量的最快途径之一：在英国和欧洲大陆，小麦仍然是主要的谷物作物，但它是六倍体（每个细胞6个基因组拷贝），这使得它作为遗传工具难以操作。大麦是北欧第三大种植谷物，虽然与小麦密切相关，但由于它是二倍体（每个细胞有两个基因组拷贝），因此在遗传上更容易处理。因此，关于大麦的知识也可以为小麦面包计划提供信息，因此大麦的工作既迅速又影响巨大。为什么是光合电子传递？光合电子传递（PET）为CO2固定提供能量，并且在谷物叶片中被很好地理解。相比之下，我们对PET在种子发育中的作用知之甚少，而这对种子的生存能力和产量也很重要。尽管不能有效地与大气交换O2或CO2，发育中的种子在其发育过程中组装并分解PET的装置。有两种假说可以解释这一现象：1)PET产生氧气，防止种子缺氧，使呼吸作用支持籽粒灌浆；2) PET产生活性氧（ROS），触发控制种子发育和后期幼苗生长的激素信号通路。种子中的光合电子传递与叶片中的不同吗？我们之前发现了一种名为TROL的PET蛋白在拟南芥（Arabidopsis）这种模式植物的抗逆性中起重要作用。我们通过敲除大麦中该蛋白的两个基因来研究这一发现是否具有农艺意义。令人惊讶的是，失去TROL并不影响叶片中的PET，但却破坏了发育中的种子中的PET。与野生型相比，突变体也表现出较低的籽粒产量和较差的种子活力。在这里提出的工作中，我们将以这些植物为工具，了解发育中的种子中的PET与叶片中的PET有何不同，并确定对种子PET独特重要的途径和成分。实验建议：准确测量PET的技术需要通过组织的透光性，这在开发谷物种子中是具有挑战性的，因为它们含有淀粉，密度大且会散射光。我们已经开发出方法来准确地做到这一点，我们的初步结果已经表明叶片和种子之间的PET存在显着差异。我们将尝试通过比较叶片和种子中PET装置的组成和结构来了解这些差异的基础。已经产生的TROL基因突变体将与其他突变体互补，以研究不同的PET途径如何影响种子产量和活力。最后，我们将确定是否可以通过在种子发育的特定点刺激trol依赖的PET通路来提高种子产量和活力。通过了解调节谷物灌浆和生存能力的触发因素，我们希望最终确定谷物产量可以抵御未来不断变化的环境的方法。

It is critical for humanity that cereal crop yields increase, and this proposal addresses factors that contribute to grain yield and viability. Photosynthetic electron transport (PET) provides the energy to fix carbon in leaves, which is transported to support grain filling. Cereal floral organs are also green, and PET in developing seeds is particularly important for yield and viability, but poorly understood. We have developed techniques and genetic tools to help fill this knowledge gap. Why barley seeds?: In the 1950s and 60s the "Green Revolution" saved millions from starvation by developing high yield cereal varieties, that were extremely efficient at transferring leaf photosynthate into developing seeds. Photosynthetic processes in cereal flower spikes are also important for high yield, and in particular the role of green tissues in developing cereal seeds remains poorly understood. Investigating this could inform breeding programs leading to further increases in grain yield. Studying barley is one of the fastest routes to improving cereal yield: In the UK and continental Europe, wheat is still the dominant cereal crop, but it is hexaploid (6 genome copies per cell) making it unwieldy as a genetic tool. Barley is the third most farmed cereal in Northern Europe and although closely related to wheat, is more genetically tractable as it is diploid (two genome copies per cell). Knowledge about barley can therefore also inform wheat breading programs, so work on barley is both rapid and high impact. Why photosynthetic electron transport? Photosynthetic electron transport (PET) provides the energy for CO2 fixation, and is well understood in cereal leaves. By contrast, we know much less about PET in developing seeds, which is also important for viability and yield. Despite not efficiently exchanging O2 or CO2 with the atmosphere, the developing seed assembles and breaks down the apparatus for PET during its development. Two hypotheses have been proposed to explain this: 1) PET produces O2, preventing hypoxia in the seed and enabling respiration to support grain filling; 2) PET produces reactive oxygen species (ROS), which trigger hormone signaling pathways that control seed development and later seedling growth.Is photosynthetic electron transport in seeds different from leaves? We previously found that TROL, a PET protein, is important for stress tolerance in Arabidopsis, a model plant. We investigated whether this finding could have agronomic importance by knocking out the 2 genes for this protein in barley. Surprisingly, loss of TROL did not affect PET in leaves, but did disrupt it in developing seeds. In comparison to wild type, the mutants also showed poor grain yield, and poor seed viability overall. In the work proposed here we will use these plants as a tool to understand how PET in the developing seed differs from PET in the leaf, and identify pathways and components that are uniquely important to seed PET. Experiments proposed: Techniques to accurately measure PET require light transmittance through tissue, which is challenging in developing cereal seeds, as they are starchy, dense and scatter light. We have developed methods to accurately do this, and our preliminary results already indicate significant differences between leaf and seed PET. We will try to understand the basis of these differences by comparing the composition and structure of the PET apparatus in leaves and seeds. The TROL gene mutants already generated will be complimented with others to examine how different PET pathways contribute to seed yield and viability. Finally, we will determine whether seed yield and viability can be improved by stimulating TROL-dependent PET pathways at specific points in seed development. By understanding the triggers that regulate grain filling and viability, we hope to eventually identify ways in which cereal yields can be future-proofed against a changing environment.