Exploiting the untapped potential of non-foliar photosynthesis in a warming world

我们对光合作用的大部分了解都来自于对树叶的研究。然而，其他植物的非叶器官(如茎、花和果实)也可以进行光合作用。麦穗是小麦植株的花朵。虽然叶片通常被认为是粮食生产中碳水化合物的唯一来源，但最近的研究结果表明，穗状光合作用对谷粒重量的贡献高达40%。然而，与树叶不同的是，尖峰光合作用对环境的反应在很大程度上是未知的。在树冠的顶部，尖峰暴露在极端的热和光下。高温--全球变暖带来的热浪的结果--破坏了关键的光合作用过程，这些过程缩短了从空气中捕获碳的高峰持续时间，导致产量严重下降。我已经开发了一种定制的成像屏幕，它揭示了叶片水平光合作用耐热性的多样性，这表明尚未开发的变异也可能存在于穗的光合作用组织中。到目前为止，还没有一种方法可以快速筛选小麦的耐热性性状。这项建议将解决缺乏有关穗耐热性的基础知识及其在极端温度下维持小麦谷物产量方面的复杂作用。这项建议采取了自上而下的方法来解决我们对高温尖峰反应知识的空白。首先，开发新的方法来快速识别穗耐热性的变异将有助于有效地评估现有小麦品种的多样性。通过将这一耐热性数据集与这些品种的遗传背景进行比较，我们可以确定这一性状的变异与小麦基因组上存在的关键遗传变异或标记之间的任何关联。这些遗传标记的识别对小麦研究界有直接的好处，从对穗耐热性遗传调控感兴趣的研究人员到选择耐热小麦品种的小麦育种者都是如此。在确定了耐热性之后，这项建议将重点放在促进现场尖峰冷却的基本机械过程上。尽管它显然很重要，但人们对尖峰与环境的物理相互作用知之甚少。随着穗的成熟，它的形状会发生变化，穗与环境的相互作用也会发生变化；不仅会影响光合作用所需的重要二氧化碳的输送，还会影响热量从基本的光合作用过程中转移出去的效率。该项目建议使用最先进的成像技术来模拟尖峰周围的空气流动，以确定改变尖峰形状如何调节热量，同时平衡碳的输送。这项基础性的探索性研究为未来评估穗状气体交换的工作奠定了基础--使研究人员能够以与叶子相同的理解深度来研究非叶结构。最后，这里开发的技术将应用于现代小麦密切相关的野生近亲的穗状结构。作为一种相对未开发的遗传多样性来源，将这些物种引入现代小麦已经发现了包括抗病在内的几个叶水平的改进。研究小麦野生相对穗的耐热性引入了另一个潜在的性状，包括在育种计划中，但也代表了这项工作的一个生态学方面，可以在未来进行探索。作为BBSRC发现研究员，我将通过最初专注于小麦穗，率先探索非叶器官的耐热性。量化和了解这一目前尚未被探索的性状的变异是至关重要的，它提供了耐热性的来源，不仅将提高我们对非叶光合作用的理解，而且随着气候变化的加速，还有助于国家和国际粮食安全。

Most of what we know about photosynthesis comes from studying leaves. However, other plant non-foliar organs (e.g. stems, flowers and fruit) are also known to photosynthesize. The wheat spike is the flower of the wheat plant. While the leaf is often assumed to be the sole-source of carbohydrates for grain production, recent results have shown spike photosynthesis contributes up to 40% to grain weight. However, unlike leaves, how spike photosynthesis responds to its environment is largely unknown.At the top of the canopy, the spike is exposed to the extremes of heat and light. High temperatures - the result of heatwaves brought about by global warming - damage key photosynthetic processes that reduce the duration of spike carbon capture from the air, leading to severe decreases in yield. I have developed a custom imaging screen which has uncovered diversity in leaf-level photosynthetic heat tolerance, suggesting that untapped variation may also reside in the spike photosynthetic tissues. To date, no methodology exists for rapidly screening wheat spikes for heat tolerance traits. This proposal will address the lack of fundamental knowledge surrounding spike heat tolerance and its complex role in maintaining wheat grain yields under extreme temperatures. This proposal takes a top-down approach to addressing the gaps in our knowledge of spike responses to heat. First, the development of novel methodology to rapidly identify variation in spike heat tolerance will facilitate efficient assessment of the diversity available in current wheat varieties. Comparing this spike heat tolerance dataset with the genetic background of these varieties allows us to identify any associations between variation in this trait and key genetic variations or 'markers' present on the wheat genome. The identification of these genetic markers is of immediate benefit to the wheat research community; from researchers interested in the genetic regulation of spike heat tolerance to wheat breeders selecting heat tolerant wheat varieties to include in breeding programs. After identification of heat tolerance, this proposal focuses on the fundamental, mechanistic processes that promote spike cooling in the field. Despite its clear importance, very little is known about the physical interaction of the spike with its environment. As the spike matures, its shape changes and so will the spikes' interaction with its environment; not only impacting on the delivery of vital carbon dioxide for photosynthesis but also how efficiently heat is transferred away from the essential photosynthetic processes. This project proposes using state-of-the-art imaging techniques to model the flow of air around the spike to determine how changing spike shape regulates heat, while balancing the delivery of carbon. This fundamental, exploratory study underpins future work into assessment of spike gas exchange - enabling researchers to investigate non-foliar structures with the same depth of understanding as leaves.Finally, the techniques developed here will be applied to the spikes of the closely related wild relatives of modern wheat. Representing a relatively untapped source of genetic diversity, introducing these species into modern wheat has already uncovered several, leaf-level improvements including disease resistance. Investigating wheat wild relative spikes for heat tolerance introduces another potential trait for inclusion into breeding programs but also represents an ecological aspect of this work which can be explored in the future.As a BBSRC Discovery Fellow, I will pioneer exploration of heat tolerance in non-foliar organs by initially focusing on the wheat spike. Quantifying and understanding variation in this currently unexplored trait is vital, providing a source of heat tolerance which will not only improve our understanding of non-foliar photosynthesis but also contribute to national and international food security as climate change accelerates.