Genomic and Functional Analysis of Circadian Rhythms and Growth Vigor in Maize

Pi：Z.Jeffrey Chen(德克萨斯大学奥斯汀分校)Copi：Frank G.Harmon(加州大学伯克利分校/USDA-ARS)生物钟协调生长和新陈代谢的空间和时间控制，导致昼夜节律和代谢稳态之间的同步相互作用。在植物中，维持强健的昼夜节律可以促进生长和健康。品系间形成的杂种或种间形成的异源多倍体通常表现出杂交优势或杂种优势：与亲本相比，杂种的生长、生物量和育性水平更高。杂种优势背后的机制还知之甚少。最近的一项研究发现，生长活力和生物钟之间存在直接联系。在拟南芥杂交种和异源四倍体中，关键的生物钟基因表达波形的改变促进了包括叶绿素生物合成和淀粉代谢在内的代谢输出。杂交种中光信号、光合作用和淀粉代谢基因的上调是由于昼夜节律时钟抑制基因的表观遗传抑制，进而导致时钟激活因子和下游代谢基因的上调。虽然在玉米中发现了基因表达、光合作用和淀粉代谢的昼夜节律，但在拟南芥杂交种和异源多倍体中发现的昼夜节律代谢活力是否直接适用于玉米等杂交作物的改良尚不清楚。玉米是研究杂种优势的最佳生物之一。此外，玉米进行C4光合作用，其特征是解剖和生化特化，在高温下增加净碳同化。在C4植物中，这种特化的一部分可能涉及时钟调节的代谢途径。该项目将测试昼夜节律如何控制玉米的新陈代谢和发育，以及昼夜节律和其他调节网络如何影响玉米杂交种的生长活力。具体目标是：(1)确定生物钟基因在包括玉米杂交种及其近交系亲本新陈代谢在内的生物途径中的直接靶点；(2)测试玉米杂交种的生物钟基因表达和生长活力如何在染色质和新陈代谢水平上受到控制；(3)阐明玉米自交系和杂交种新陈代谢和生长势的昼夜调节的分子基础。这项研究的影响对许多基本生物学领域具有变革性的影响，从1726年在向日葵植物中首次发现的昼夜节律到杂交活力或杂种优势，这是一种引起包括查尔斯·达尔文在内的许多科学家感兴趣的普遍现象。这项工作的结果直接影响到杂交作物的改良，尤其是对农业、粮食安全、生物燃料和人类健康至关重要的玉米和高粱。对植物杂交种代谢活力的昼夜节律的机械洞察也适用于在其他有性繁殖生物如人类中发现的新陈代谢和生理的昼夜节律。在外展和培训方面，该项目将通过UTeach计划为未来的科学教师提供暑期学生实习机会。德克萨斯大学奥斯汀分校(UT Austin)开发了UTeach项目，全国许多其他机构都在效仿。此外，该项目将为阿尔康州立大学和密西西比山谷州立大学这两所历史上的黑人学院/大学的理科硕士(MSc)学生提供研究培训机会。序列数据将通过GEO、MaizeGDB和Gramene向公众开放。在这个项目中产生的种子和有关种质的信息的请求将通过MaizeGDB获得。

PI: Z. Jeffrey Chen (The University of Texas at Austin) CoPI: Frank G. Harmon (University of California - Berkeley/USDA-ARS) Biological clocks orchestrate spatial and temporal control of growth and metabolism, leading to synchronous interactions between circadian rhythms and metabolic homoeostasis. In plants, maintenance of robust circadian rhythms promotes growth and fitness. Hybrids formed between strains or allopolyploids formed between species often show hybrid vigor or heterosis: superior levels of growth, biomass, and fertility in the hybrids compared to the parents. The mechanisms underlying heterosis are poorly understood. A recent study found a direct link between growth vigor and the circadian clock. Alterations in the expression waveform of key circadian clock genes in Arabidopsis hybrids and allotetraploids promote metabolic outputs including chlorophyll biosynthesis and starch metabolism. Upregulation of light signaling, photosynthesis, and starch metabolic genes in hybrids results from epigenetic repression of the circadian clock repressor genes during the day that, in turn, causes upregulation of clock activators and downstream metabolic genes. Although diurnal rhythms in gene expression, photosynthesis, and starch metabolism have been documented in maize, it is unknown whether the circadian-mediated metabolic vigor found in Arabidopsis hybrids and allopolyploids is directly applicable to the improvement of hybrid crops such as maize. Maize is among the best organisms for studying heterosis. Moreover, maize performs C4 photosynthesis, characterized by anatomical and biochemical specialization that increases net carbon assimilation at high temperatures. Part of this specialization in C4 plants may involve clock-regulated metabolic pathways. This project will test how circadian rhythms control metabolism and development in maize, as well as how circadian and other regulatory networks affect growth vigor in maize hybrids. Specific objectives are to (1) determine direct targets of clock genes in biological pathways including metabolism in maize hybrids and their inbred parents; (2) test how circadian clock gene expression and growth vigor in maize hybrids are controlled at levels of chromatin and metabolism; and (3) elucidate molecular bases for circadian regulation of metabolism and growth vigor in maize inbreds and hybrids.The impact of this research is transformative for many fundamental areas of biology ranging from circadian rhythms, first discovered in heliotrope plants in 1726, to hybrid vigor or heterosis, a widespread phenomenon that has intrigued many scientists, including Charles Darwin. The results from this work impact directly on improvement of hybrid crops, most notably maize and sorghum, which are of great importance to agriculture, food security, biofuels, and human health. Mechanistic insights into circadian regulation of metabolic vigor in plant hybrids are also applicable to the circadian rhythms in metabolism and physiology found in other sexually reproducing organisms like humans. With regard to outreach and training, this project will provide summer student internships for future science teachers through the UTeach program. The University of Texas at Austin (UT Austin) developed the UTeach program, and many other institutions across the country have replicated it. In addition, the project will provide research training opportunities for Master of Science (MSc) students at Alcorn State University and Mississippi Valley State University, two Historically Black Colleges/Universities. Sequence data will be available for public through GEO, MaizeGDB, and Gramene. Requests for seed and information about germplasm generated in this project will be available through MaizeGDB.