Clegg M T, Durbin M L
Department of Botany and Plant Sciences, University of California, Riverside, CA 92521-0124, USA.
Proc Natl Acad Sci U S A. 2000 Jun 20;97(13):7016-23. doi: 10.1073/pnas.97.13.7016.
We review the study of flower color polymorphisms in the morning glory as a model for the analysis of adaptation. The pathway involved in the determination of flower color phenotype is traced from the molecular and genetic levels to the phenotypic level. Many of the genes that determine the enzymatic components of flavonoid biosynthesis are redundant, but, despite this complexity, it is possible to associate discrete floral phenotypes with individual genes. An important finding is that almost all of the mutations that determine phenotypic differences are the result of transposon insertions. Thus, the flower color diversity seized on by early human domesticators of this plant is a consequence of the rich variety of mobile elements that reside in the morning glory genome. We then consider a long history of research aimed at uncovering the ecological fate of these various flower phenotypes in the southeastern U.S. A large body of work has shown that insect pollinators discriminate against white phenotypes when white flowers are rare in populations. Because the plant is self-compatible, pollinator bias causes an increase in self-fertilization in white maternal plants, which should lead to an increase in the frequency of white genes, according to modifier gene theory. Studies of geographical distributions indicate other, as yet undiscovered, disadvantages associated with the white phenotype. The ultimate goal of connecting ecology to molecular genetics through the medium of phenotype is yet to be attained, but this approach may represent a model for analyzing the translation between these two levels of biological organization.
我们回顾了将牵牛花的花色多态性作为适应性分析模型的研究。从分子和遗传水平到表型水平，追踪了决定花色表型的途径。许多决定黄酮类生物合成酶成分的基因是冗余的，但是，尽管存在这种复杂性，仍有可能将离散的花表型与单个基因联系起来。一个重要的发现是，几乎所有决定表型差异的突变都是转座子插入的结果。因此，这种植物早期人类驯化者所利用的花色多样性是牵牛花基因组中丰富多样的移动元件的结果。然后，我们考虑了一段旨在揭示美国东南部这些各种花表型生态命运的悠久研究历史。大量研究表明，当种群中白色花朵稀少时，昆虫传粉者会歧视白色表型。由于这种植物是自交亲和的，传粉者偏好会导致白色母本植物自花受精增加，根据修饰基因理论，这应该会导致白色基因频率增加。地理分布研究表明，白色表型还存在其他尚未发现的劣势。通过表型将生态学与分子遗传学联系起来的最终目标尚未实现，但这种方法可能代表了一种分析这两个生物组织层次之间转化的模型。
