Comparative and Functional Analysis of a Genetic Pathway Controlling Floral Asymmetry

尽管在了解基因如何影响特征的发育方面已经取得了很大进展，例如花中的器官或苍蝇的眼睛，但我们对这些特征最初是如何进化的仍然知之甚少。自达尔文以来，人们一直认为，小说中的人物并不是完全重新出现的，而是通过修改或修补以前已经存在的东西而出现的。我们现在知道，这种修修补补涉及到基因的变化，但这种变化究竟如何导致新的人物或特征的产生仍有待阐明。解决这个问题的一种方法是以一种新的特征为例，了解它是如何在具有该特征的物种中受到基因控制的，然后将其与缺乏该特征的物种的情况进行比较。通过定义允许一个物种而不是另一个物种产生这种特征的遗传差异，应该可以理解特定的成分可能发生了什么变化，从而使新奇的角色在进化过程中出现。在这项建议中，我们选择分析植物的一个关键性状-花不对称的进化。许多花，如金凤花，都是径向对称的，在花周围都有相似的花瓣。其他花种，如兰花和金鱼草，具有不对称的花，其上部花瓣与下部花瓣非常不同。这种不对称状态被认为在开花植物中独立地从对称状态进化了许多次，作为对传粉者的特殊适应。研究得最好的花不对称案例是金鱼草，在那里已经分离和分析了调节这一过程的四个关键基因。然而，进一步研究这些基因的一个困难是无法将这些基因的修改版本引入金鱼龙。最近，一种方便地将基因导入金鱼龙的新方法的开发克服了这一障碍。这项建议的目的是利用这一进展进一步分析控制金鱼花不对称的基因是如何发挥作用的，并将其与拟南芥的情况进行比较，拟南芥是一种具有放射状对称花朵的植物，因此代表着一种更古老的状态。这应该会对如何通过基因变化衍生出新奇的人物提供重要的见解。

Although much progress has been made in understanding how genes influence the development of characters, such as the organs in a flower or the eye of a fly, we still know little about how such characters evolved in the first place. Ever since Darwin, it has been thought that novel characters do not emerge completely anew but through modification or tinkering with what was already there before. We now know that this tinkering involved changes in genes but precisely how such changes can lead to the production of novel characters or traits still remains to be elucidated. One way of approaching this problem is to take an example of a novel trait, understand how it is genetically controlled in a species that has the trait and then compare this to the situation in a species that lacks the trait. By defining the genetic differences that allow one species but not the other to produce the trait, it should be possible to understand how particular components may have changed so as to allow the novel character to have emerged during evolution. In this proposal we have chosen to analyse the evolution of a key trait in plants - flower asymmetry. Many flowers, such as buttercups, are radially symmetrical, having similar petals all the way round the flower. Other flower species, such as orchids and snapdragons, have asymmetric flowers in which the upper petals are very different from the lower ones. This asymmetric condition is thought to have evolved many times independently in flowering plants from the symmetrical state as a specialized adaptation to pollinators. The best studied case of floral asymmetry is in the snapdragon (Antirrhinum) where four key genes that regulate the process have been isolated and analysed. However, one difficulty with studying these genes further has been the inability to introduce modified versions of the genes into snapdragons. This obstacle has recently been overcome by the development of a new way of conveniently introducing genes into snapdragons. The aim of this proposal is to exploit this development to analyse further how genes controlling floral asymmetry work in snapdragons and to compare this to the situation in Arabidopsis, a plant that has radially symmetrical flowers and therefore represents a more ancestral condition. This should give important insights into how novel characters can be derived through genetic change.