Transcribed Microsatellites as Engines of Adaptive Change; Testing the "Tuning Knob" Hypothesis in Natural Populations of the Annual Sunflower, Helianthus annuus

微卫星是在整个生物体基因组中发现的高度重复的DNA序列。这些序列具有非常高的突变率，可以改变微卫星的物理长度。在它们首次被发现后，人们认为微卫星只会在基因组的非功能区域发现，因为它们可能会破坏正常的基因功能。事实上，已知最早描述的一些微卫星会导致神经退行性疾病，如亨廷顿舞蹈病。然而，我们现在知道，许多物种中有成千上万的基因包括微卫星。基因中微卫星的普遍存在意味着许多可能是功能性的。这个项目的重点是微卫星在改变向日葵基因表达方式方面可能发挥的作用。研究人员正在测试微卫星突变改变向日葵基因表达水平的假设，这表明这类微卫星可以促进进化变化。鉴于其突变率，微卫星可能代表基因组中进化最快的基因调控元件。如果这个假设是正确的，那么微卫星长度应该与基因表达水平相关。此外，如果选择作用于这种变异源，那么自然种群中的等位基因频率应该反映这些过程。接受这些机制将表明，种群获得新的和可遗传的变异的速率比通常假设的要高得多。更广泛的影响：本项目支持本科生研究人员。高级研究人员将向生物学专业的学生介绍先进的计算方法，而对计算生物学感兴趣的计算机科学专业的学生将参与数据收集和分析。此外，学生培训的一个主要重点是发展他们的拨款写作和数据分析技能，以及科学研究成果的展示。学生们将在科学会议上展示他们的发现，并共同撰写研究期刊文章。此外，密西西比州立大学是全国研究型大学中少数民族比例最高的大学之一，目前正在实施旨在将少数民族纳入这一项目的战略。

Microsatellites are highly repetitive DNA sequences found throughout organismal genomes. These sequences have very high mutation rates that change the physical length of the microsatellite. After they were first discovered, it was assumed that microsatellites would only be found in nonfunctional regions of genomes because they would likely disrupt normal gene function. In fact, some of the earliest microsatellites described are known to cause neurodegenerative diseases, like Huntington's chorea. However, we now know that many thousands of genes in many species include microsatellites. The prevalence of microsatellites in genes implies that many may be functional. This project focuses on the role microsatellites might play in altering how genes are expressed in sunflowers. The researchers are testing the hypothesis that microsatellite mutations alter gene expression levels in sunflowers, suggesting that this class of microsatellite can facilitate evolutionary change. Given their mutation rates, microsatellites may represent the most rapidly evolving gene regulatory elements in genomes. If this hypothesis is true, then microsatellite lengths should correlate with gene expression levels. Further, if selection is acting on this source of variation, then allele frequencies in natural populations should reflect these processes. Acceptance of these mechanisms would suggest that populations acquire novel and heritable variation at rates much higher than typically assumed.Broader Impacts: This project supports undergraduate student researchers. Senior researchers will expose biology students to advanced computational methods, and computer science majors interested in computational biology will be involved in the collection of data and analysis. In addition, a major focus of student training is the development of their grant writing and data analysis skills, and the presentation of scientific research findings. Students will present their findings at scientific meetings and coauthor research journal articles. Further, Mississippi State University has one of the highest percentages of minorities among research universities in the country, and strategies designed to include minorities in this project are being pursued.