PGI Gene Sequences and Phylogenetic Inferences in Clarkia

进化生物学已经在加州一年生植物Clarkia （onagracae）中进行了40年的研究，该属为研究物种起源、自然种群的遗传变异以及最近的分子进化提供了许多模型系统。分子研究开始确定复制的细胞质磷酸葡萄糖异构酶（PGI）的起源模式，这些酶存在于12种克氏菌中，但在其他12种克氏菌中不存在。PGI催化糖代谢的重要反应。迄今为止，一些PGI基因已被部分测序。它们具有非常复杂的结构，有19个外显子（和18个内含子）编码约88%的PGI蛋白（483/550个氨基酸），是已知的任何植物基因中外显子数量最多的。另一种克氏菌叶绿体PGI同工酶的编码基因也已测序；它有一个连续的开放阅读框，没有外显子。在目前的项目中，将克隆和测序其他编码克拉氏菌同工酶的PGI基因，并对其进行测序。来自这些序列的证据将用于确定这种重复是否发生在属进化的早期，并在一些谱系中保留，但在其他谱系中消失，或者它是否出现在最近。由于重复的pgi在4个分类区段中具有物种特征，而在另外3个区段中不存在，因此该证据有望解决区段之间的系统发育关系，尽管对克氏菌进行了深入研究，但这一问题仍然难以解决。序列证据还将用于比较质体和细胞质pgi之间差异的速率和数量。该分析将有助于理解产生分子分化的机制，并构成迄今为止对编码蛋白质的植物核基因进化的少数研究之一。

Evolutionary Biology has been studied in the California annual plant Clarkia (Onagraceae) for four decades and the genus has provided a number of model systems in which to study the origin of species, genetic variation in natural populations and, more recently, molecular evolution. The molecular studies were initiated to determine the mode of origin of the duplicated cytosolic phosphoglucose isomerase (PGI) siozymes that are present in 12 Clarkia species but absent in 12 others. PGI catalyzes an essential reaction in sugar metabolism. To date, several PGI genes have been partially sequenced. They have remarkably complex structure with 19 exons (and 18 introns) so far identified encoding about 88% of the PGI protein (483/550 amino acids), the largest number of exons known for any plant gene. A gene encoding the chloroplast PGI isozyme from a different Clarkia has also been sequenced; it has a continuous open reading frame with no exons. During the current project, additional PGI genes encoding both isozymes from clarkias with and without the duplication will be cloned and sequenced. Evidence from the sequences will be used to determine whether the duplication occurred early in the evolution of genus and was retained in some lineages but lost in others or whether it arose more recently. Since duplicated PGIs characterize species in four taxonomic sections but are absent in three other sections, the evidence can be expected to resolve the phylogenetic relationships among the sections, a problem that has remained refractory even though Clarkia has been studied intensively. The sequence evidence will also be used to compare the rate and amount of divergence between the plastid and cytosolic PGIs. The analysis will contribute to understanding the mechanisms that generate molecular divergence and constitutes one of the few studies to date of the evolution of plant nuclear genes encoding proteins.