Molecular Studies of PgiC Evolution in Allotetraploid Species of Clarkia (Onagraceae)

月见草科（月见草科）的Clarkia属是一个由42个物种组成的群体，除了一个外，其他物种都原产于北美西部，作为理解物种形成和遗传分化的模型，以及评估不同来源的证据对推断系统发育的价值，人们已经对其进行了50多年的研究。通过对植物糖代谢必需酶磷酸葡萄糖异构酶胞质同工酶基因PgiC的核苷酸序列分析，确定了植物间的家谱关系。PgiC在产生克氏菌的基础种群中有重复，现存的二倍体物种中约有一半表达这两个重复的基因（具有两个PgiC同工酶）。在其他二倍体物种中，一个PgiC基因被“沉默”（只有一个同工酶存在于酶的功能中，但有两个可检测的DNA位点）。克氏菌还包括许多异源四倍体物种，它们通过杂交将两个二倍体物种的基因组（染色体组）结合在一起，因此预计具有四个PgiC基因。然而，在所有四倍体克拉氏菌中，只发现了两个PgiC基因。Gottlieb教授研究的主要目标是通过DNA核苷酸测序确定哪些PgiC基因表达，以及未表达的基因是否发生突变或丢失。在本研究中，将自然产生的四倍体物种与实验合成的二倍体祖先之间的杂种进行比较。此外，二倍体和四倍体之间的杂交将被研究。合成的杂交种有望表达其亲本的所有PgiC基因。将比较二倍体和四倍体基因组中重复基因的核苷酸分化程度和速率。本研究试图在分子水平上描述在异源四倍体植物物种形成和建立过程中编码已知功能酶的特定基因的命运。这些基本信息也应该有助于指导未来对基因沉默和丢失的分子原因的分析。该研究还将为多倍体核基因在系统发育分析中的应用提供信息，这是植物系统学中一个高度相关的问题，因为超过一半的开花植物是多倍体。

9615037 Gottlieb The genus Clarkia of the evening-primrose family (Onagraceae) is a group of 42 species, all but one native to western North America, that has been examined for more than 50 years as a model for understanding speciation and genetic divergence and to assess the value of different sources of evidence for inferring phylogeny. The genealogical relationships among the species have been resolved by analyses of many classes of characters, including nucleotide sequences of the gene PgiC which encodes the cytosolic isozyme of phosphoglucose isomerase, an essential enzyme of sugar metabolism in plants. PgiC was duplicated in the basal stock that gave rise to Clarkia, and about half the extant diploid species express both duplicated genes (have two PgiC isozymes). In the other diploid species, one PgiC gene has been "silenced" (there is only one isozyme present for enzyme function, but there are two detectable DNA loci). Clarkia also includes a number of allotetraploid species, that combine through hybridization the genomes (chromosome sets) of two diploid species and are thus expected to possess four PgiC genes. However, in all tetraploid Clarkias tested only two PgiC genes have been found. The major goal of Prof. Gottlieb's research is to determine through DNA nucleotide sequencing which PgiC genes are expressed and whether the genes that are not expressed have been mutated or lost. In this study, the naturally occurring tetraploid species will be compared to experimentally synthesized hybrids between their diploid progenitors. In addition, hybrids between the diploids and tetraploids will be studied. The synthesized hybrids are expected to express all the PgiC genes of their parents. The extent and rate of nucleotide divergence between the duplicate genes will be compared between the diploid and tetraploid genomes. The proposed studies are an attempt to describe at the molecular level the fate of particular genes encoding enzymes of known function during the formation and establishm ent of allotetraploid plant species. Such basic information should also help guide future analysis of the molecular causes of gene silencing and loss. The study will also provide information about the use of nuclear genes from polyploids in analyzing phylogeny, a highly relevant issue in plant systematics because more than half of the flowering plants are polyploid.