RESEARCH INITIATION - Using Gene Trees to Uncover the Role of Hybridization and Polyploidy in Leucaena (Fabaceae)

智力价值：染色体组的复制(多倍体)和种间杂交是已知的产生新的基因类型和物种多样性的关键机制。此外，基因组技术和数据分析的最新进展表明，多倍体和杂交在重大进化事件中发挥的基础作用比以前认识的更多。这些发现以及这些机制导致的巨大后果表明，当涉及到我们对杂交和多倍体的分布及其潜在作用的理解时，我们只是触及了冰山一角。在这个提案中，我概述了一个项目，其目标是促进对这些现象分布的理解，以及在专注于密切相关植物物种之间关系的研究项目中应用新工具。通过这项工作，我打算阐明豆科银合欢属发散种和网状种之间的关系，这一组一直是我最近研究计划的重点，并将成为未来研究的核心组成部分。研究系统：银合欢22种包括假定存在的发散的二倍体祖先，具有衍生的杂交种、同源多倍体和异源多倍体起源的分类群/个体，都在相当有限的地理分布内。银合欢属(Fabaceae)植物间杂交和多倍体现象的普遍存在，使其成为植物进化生物学研究的重要系统。此外，由于与正在进行的本土植物驯化以及一些分类群作为热带入侵杂草的地位有关，人们对银合欢的系统研究产生了普遍的兴趣。一些研究试图阐明银合欢属多倍体和杂交物种的起源；然而，缺乏足够可变的数据继续阻碍明确支持的假说的发展，这些假说对于理解银合欢多倍体和杂交物种的起源以及随后这些机制对进化的具体影响至关重要(S)。目的：本建议的具体研究目标是：1)使用一种新的策略来从银合欢中建立多个充分可变的基于DNA序列的数据集，以充分研究分类群之间的分化和网状关系；2)展示基于SCAR的新策略在系统发育研究中的实用性；3)完成一个基于网络的数据库，这将有助于将越来越多的关于银合欢的信息传播到更广泛的研究社区；以及4)教育和激励来自少数群体服务机构的本科生和研究生参与者。广泛的影响：这项研究的发现将为杂交和多倍体在主要是新热带树种中的一般作用提供关键证据，其中包括正在驯化的物种。此外，开发的工具将有助于解决被子植物系统学中常见的系统发育问题。这一项目的资助和实施将为少数群体服务机构的研究生和本科生创造培训和教育机会，这些机构设在一个实验室，有吸引和培训代表少数群体的个人的记录。所有参与这个项目的学生将发展分类学、分类学、分子生物学和生物信息学方面的专业知识。此外，关于银合欢的数据库的建成将为这个正在开发的系统提供一个全面的全球信息资源，这将理想地吸引其他有兴趣利用银合欢研究杂交、多倍体和驯化的基因组影响的研究人员的注意。

Intellectual Merit: The duplication of chromosome sets (polyploidy) and interspecific hybridization are critical mechanisms known to generate novel genotypes and species diversity. Furthermore, recent advances in genomic techniques and data analysis have suggested that polyploidy and hybridization played more fundamental roles in major evolutionary events than previously recognized. These discoveries along with the tremendous range of consequences induced by these mechanisms identify that we are only touching the tip of the iceberg when it comes to both our understanding of the distribution of hybridization and polyploidy and their potential actions. In this proposal I outline a project whose goals are to advance the understanding of the distribution of these phenomena as well as the application of new tools in research programs focused on relationships among closely related plant species. Through this work I intend to elucidate relationships among divergent and reticulate species in the legume genus Leucaena, a group that has been a focus of my recent research program and that will form a core component of future studies.The Study System: The 22 species of Leucaena include presumed extant divergent diploid progenitors with derived taxa/individuals of hybrid, autopolyploid, and allopolyploid origins all within a fairly restricted geographic distribution. The prevalence of hybridization and polyploidy among species of Leucaena (Fabaceae) help to make it an important system in the study of plant evolutionary biology. In addition, general interest in systematic research on Leucaena has been sparked by connections to ongoing indigenous plant domestication and the status of some taxa as invasive weeds in the tropics. Several studies have attempted to elucidatethe origins of polyploid and hybrid species of Leucaena; however, a lack of sufficiently variable data continues to hinder the development of clearly supported hypotheses that are critical for the understanding of their origin(s) and subsequent study on the specific impact of these mechanisms on evolution.Objectives: The specific research objectives of this proposal are to: 1) use a novel strategy to develop multiple sufficiently variable DNA sequence based data sets from Leucaena to fully investigate divergent and reticulate relationships among taxa; 2) demonstrate the utility of the novel SCAR-based strategy in phylogenetic studies; 3) complete a web-based database that will facilitate the dissemination of the growing body of information on Leucaena to the broader research community; and 4) educate and inspire undergraduate and graduate student participants from a minority serving institution.Broader impacts: Findings from this study will provide critical evidence for the general role of hybridization and polyploidy in a genus of chiefly neotropical trees that includes species undergoing domestication. In addition, the tools developed will help to address problems resolving phylogenies that have been commonplace in angiosperm systematics. The funding and implementation of this project will generate training and educational opportunities for graduate and undergraduate students at a minority serving institution in a laboratory with a record of attracting and training individuals who represent minority groups. All students involved in this project will develop expertise in taxonomy, systematics, molecular biology, and bioinformatics.Furthermore, the completion of the data base on Leucaena will supply a comprehensive global resource for information on this developing system that will ideally attract the attention of other researchers interested in using Leucaena to study the genomic impacts of hybridization, polyploidy, and domestication.