Phylogenetics and Plastid Genome Evolution of Vanilloideae (Orchidaceae)

纽约植物园的Kenneth M. Cameron博士获得了一笔赠款，以继续他对兰花亚科Vanilloideae的进化和分类进行实验室和实地研究，其中包括香草兰（Vanilla planifolia）——在大约25,000种兰花中唯一具有重要农业价值的兰花。它们被认为是一种古老的相对原始的兰花，分布在世界各地。它们一直被认为是充分理解大型兰花家族的进化和分类的关键，但它们抵制了将它们硬塞进传统亚科的尝试。卡梅隆博士之前的分子研究表明，这些香草兰花代表了一个独立的、独特的亚科，是除两个属外所有兰花中最原始的。然而，亚科内的物种关系仍不清楚。这些发现强调了这些植物在进化中所占据的关键地位，以及进一步深入系统研究的必要性。具体来说，研究将包括一个分子组成部分，将重点放在构建一个坚实的进化树亚家族使用DNA序列从一套核，叶绿体和线粒体基因。然而，分子方面的项目将不限于DNA测序。此外，我们还将从叶绿体基因组中选择基因及其产物进行详细的研究，以更好地了解寄生于土壤真菌上的非绿色类群光合机构退化的模式和过程。卡梅伦博士已经研究了三种不同类型的光合作用基因，并发现其中两种（rbcL和psaB，但不包括atpB）在一些非光合作用类群中存在显著缺失，而在其他类群中则存在极高的突变率。这些发现表明，香兰科植物正处于叶绿体基因组降解的早期阶段。因此，它们是研究这种生物现象的理想生物群体。最后，在分子研究的基础上，开展本类群花形态和传粉生物学的新研究。许多香草类群的特征是复杂的花，具有突出的花瓣纹饰，以可移动的鳞片和刚毛的形式。特别是这些结构，不同于兰花家族中的任何其他结构。为了理解它们的形式、功能和进化起源，它们值得仔细研究。香兰科植物长期以来一直被认为是一种具有经济价值和独特的植物群，但它们的自然历史的几个方面一直是生物学家争论的来源。毫无疑问，对这一关键群体的更全面的了解将对我们理解地球上第二大开花植物家族的进化和多样性有价值。尽管香草对人类具有重要的经济意义，但很少有对这些植物进行全面系统的调查。比较形态学、解剖学和传粉研究也缺乏。由于这些原因，这些形态学和分子研究的综合结果应该为香兰科植物的命名问题、生物地理模式、花形态趋势和基因组进化提供一个坚实的系统发育研究。很少有香草兰科植物适合栽培。因此，许多物种濒临灭绝或已经灭绝。因此，如果要在兰花因习性破坏和过度采集而丧失之前，了解它们与真菌和动物传粉者之间独特的相互作用，就必须对这一迷人而关键的兰花群进行系统的研究。

A grant has been awarded to Dr. Kenneth M. Cameron at The New York Botanical Garden to continue his laboratory and field studies on the evolution and classification of the orchid subfamily Vanilloideae, which includes Vanilla planifolia -- the only orchid species out of approximately 25,000 that has significant agricultural value. These are considered an ancient lineage of relatively primitive orchids that are found worldwide in distribution. They have always been considered critical to fully understanding the evolution and classification of the large orchid family, but have resisted attempts to shoehorn them into traditional subfamilies. Previous molecular research by Dr. Cameron has shown these vanilloid orchids to represent a separate, distinct subfamily that is the most primitive of all but two genera of orchids. However, the relationships of the species within the subfamily are still unclear. These findings emphasize the evolutionarily pivotal position occupied by these plants and the need for further, in-depth systematic investigation. Specifically, the research will include a molecular component that will focus on constructing a solid evolutionary tree for the subfamily using DNA sequences from a suite of nuclear, chloroplast, and mitochondrial genes. However, the molecular aspect of the project will not be limited to DNA sequencing. In addition, select genes and their products from within the chloroplast genome will be studied in detail to better understand the pattern and process of degeneration of the photosynthetic apparatus among the non-green taxa that live as parasites on soil fungi. Already, Dr. Cameron has investigated three different classes of photosynthesis genes, and has discovered that two of the three (rbcL and psaB, but not atpB) are characterized by significant deletions in some of the non-photosynthetic taxa, and extremely high rates of mutation in others. These findings suggest that the vanilloid orchids are in the early stages of chloroplast genome degradation. They are, therefore, an ideal group of organisms in which to study this biological phenomenon. Finally, in addition to molecular research, new studies on floral morphology and pollination biology in the group will be initiated. Many of the vanilloid taxa are characterized by complex flowers with prominent petal ornamentation in the form of mobile scales and bristles. These structures, in particular, are unlike any other in the orchid family. They deserve careful examination in order to understand their form, function, and evolutionary derivation. The vanilloid orchids have been long recognized as an economically valuable and unique group of plants, but several aspects of their natural history have been the source of controversy among biologists. A more thorough knowledge of this pivotal group undoubtedly will be valuable to our understanding of the evolution and diversity within the second largest family of flowering plants on Earth. Despite the economic importance of Vanilla to humankind, there exist few thorough systematic investigations of these plants. Comparative morphological, anatomical, and pollination studies of the group are also lacking. For these reasons, the combined results of these morphological and molecular studies should provide a solid phylogeny of Vanilloideae for which nomenclatural issues, patterns of biogeography, trends in floral morphology, and genome evolution can be examined. Few of the vanilloid orchid species take to cultivation. As a consequence, many are endangered or already extinct. It is imperative and warranted, therefore, that systematic research continues on this fascinating and pivotal group of orchids if their unique interactions with fungi and animal pollinators are to be understood before they are lost to habit destruction and overcollecting.