Evolution of temperature-mediated flowering in grasses

在温带地区，全球变暖已经导致冬季缩短，并被极端天气事件打断，比如不合时宜的高温。虽然温暖的温度通常可以刺激快速生长，但许多温带植物将低温作为准备开花的暗示，这一事实使得很难预测变暖对其繁殖产量的影响。幸运的是，对植物适应过去气候变化的研究可以为预测未来的气候变化提供信息。本研究旨在剖析具有重要经济意义的草科植物对高温和低温的开花反应的进化史，并确定这些反应背后的基因。该项目的结果将是更好地理解极端温度如何以及为什么影响适应不同气候的草物种的开花，以及发现新的开花时间基因，这些基因可以用于作物育种。教学和研究的结合，以温度调节的草类开花为中心，也将为下一代科学家提供丰富的机会，他们负责解决世界上一些最紧迫的问题。在许多温带作物中，包括禾本科、小麦和大麦，花能力的获得是对冰点以上低温的长时间响应（春化），从而允许随着春天的到来而快速开花。现有证据表明，春化反应的单一起源存在于约3800个包含Pooideae的物种的祖先中，而在其他大型PACMAD草枝中至少有一个独立的起源。这两组植物的开花途径似乎都是通过转录因子中果实（FUL）分支基因的表观遗传修饰来传递寒冷信号的，因此染色质的时间依赖性修饰导致了对冬天的“记忆”。在一些不春化反应的小麦品种中，高温也可以触发FUL转录，而在春化反应的品种中，高温会导致去春化和开花延迟。尚不清楚的是，祖先草是否以及如何将温度线索整合到其开花途径中，春化和去春化的独立起源是否通过招募相似的基因和调节元件而进化，以及温度调节开花进化的历史对于草对未来天气事件的适应性意味着什么，这些天气事件被预测将变得越来越不稳定和极端。为了解决这些问题，该项目将结合生长实验、时空比较转录组学和基于crispr的功能分析，以深入了解不同草系中低温和高温途径之间的串音引起的适应性限制，并分离出新的温度调节开花时间基因和调控区域，这些基因和调控区域可能用于谷物改良。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In temperate regions, global warming is already causing shortened winters that are interrupted by extreme weather events, such as unseasonably warm temperatures. Although warmer temperatures can often stimulate rapid growth, the fact that many temperate plants use low temperatures as a cue to prepare for flowering makes it difficult to predict the consequences of warming on their reproductive yield. Luckily, studies of plant adaptations to past climate change can be informative for predicting what will happen in the future. This proposal aims to dissect the evolutionary history of flowering responses to high and low temperatures in the economically important grass family, and to determine the genes underlying these responses. Outcomes of the project will be a better understanding of how and why temperature extremes affect flowering in grass species adapted to different climates, and the discovery of novel flowering time genes that can be targeted in crop breeding. The integration of teaching and research, centered around temperature-regulated flowering in grasses, will also provide rich opportunities to the next generation of scientists charged with solving some of the world’s most pressing problems.In many temperate crops, including the Pooideae grasses wheat and barley, the attainment of floral competency occurs in response to extended periods of above freezing cold (vernalization), thus allowing rapid flowering with the onset of spring. Available evidence suggests a single origin of vernalization responsiveness in the ancestor of the ~3,800 species containing Pooideae, with at least one independent origin in the other large PACMAD grass clade. The flowering pathway of both groups appears to relay the cold signal through the epigenetic modification of genes within the FRUITFULL (FUL) clade of transcription factors, whereby time-dependent modifications to chromatin result in a ‘memory’ of winter. In some non-vernalization responsive cultivars of wheat, FUL transcription can also be triggered by high temperatures, whereas in vernalization responsive cultivars high temperatures cause devernalization and delayed flowering. What is not well understood is if and how the ancestral grass integrated temperature cues into its flowering pathway, whether independent origins of vernalization and devernalization evolved through the recruitment of similar genes and regulatory elements, and what the history of temperature-regulated flowering evolution means for adaptability of grasses to future weather events that are predicted to become increasingly erratic and extreme. To address these questions, this project will combine growth experiments, spatiotemporal comparative transcriptomics, and CRISPR-based functional analyses to provide insight into adaptive constraints caused by cross-talk between the low and high temperature pathways in distinct grass lineages, and to isolate novel temperature-regulated flowering time genes and regulatory regions that can potentially be used for cereal improvement.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.