The Primula S locus: gene function and the maintenance and breakdown of heterostyly

授粉很重要，我们70%的食物直接来自授粉，如种子、谷物、水果和浆果。这对植物的繁殖也很重要，这不仅会产生下一代，还会产生自然选择可以采取行动的变异。这种变异使植物能够适应不断变化的环境，并在新的栖息地定居。大多数植物产生两性花，但植物不能移动或主动选择伴侣，相反，它们进化出了有趣的策略，以防止自花授粉和促进异花授粉。这些策略中最引人注目的一种是异型花柱，它使用昆虫传粉者(异型=不同；风格=雌性结构)。查尔斯·达尔文观察到报春花有两种形式的花，花柱长而雄蕊短，线形花柱短，雄蕊长。这些相互的位置促进了昆虫访客在每种花类型之间的花粉转移。一组统称为S基因的基因控制着这两种花的发育。早期植物学家和遗传学家对报春花进行科学研究的丰富历史使其成为植物育种系统的重要教科书范例。我们的研究将通过使用最新的研究工具来探索异型花是如何产生的，它是如何被控制的，以及为什么它偶尔会出错。我们对报春花(Primula Uggaris)的基因组进行了测序，并确定了一组控制其两种花型发育的五个基因。这些基因只在线穗中发现，而在针叶植物中不存在。只有那些继承了这个基因簇的个体才能产生线穗花朵。我们的研究表明，我们认为导致线虫草花雄蕊伸长的基因出现在大约5170万年前，在所有现代报春花物种的祖先中。我们还发现了控制花柱长度的基因。该基因簇包含另外三个基因，在本研究中，我们将对它们的功能进行表征，以确定它们如何共同作用来控制针形和线形花朵的花结构，从而促进报春花的昆虫介导的授粉。在过去的5170万年里，报春花的30个不同物种已经失去了产生两种类型的花的能力，它们都具有长花柱和长雄蕊，并且永远不会产生短花柱的花。这些同源异型不使用昆虫传粉者，而是自交。我们的研究表明，在这些物种中，控制花柱长度的基因已经丢失或损坏。这些同源物种提供了一个令人兴奋的机会，来探索一个基因是如何随着时间的推移，在不同报春花物种的进化过程中，在多个不同的场合丢失或损坏的。这一点很重要，因为了解发展是如何出错的，有助于解释它是如何正常运作的。我们将利用我们的报春花基因组序列来鉴定和表征这些不同报春花物种中相应的S基因簇，以发现导致异型花柱丧失的基因突变。大多数植物和动物的基因存在于两个副本中，一个来自母亲，一个来自父亲；这是很有用的，如果一个副本受损，第二个副本充当备份，因此功能得以保留，它还可以使用另一个作为模板修复受损的副本。这种安排提供了代代相传的遗传稳定性。从我们对报春花异型花柱控制基因的研究中，一个非常令人惊讶的发现是，它们只以单一拷贝的形式存在，没有备份拷贝。因此，异型花柱是稳定的，这是令人惊讶的，因为关键基因的任何遗传损伤都无法修复。我们还没有对这个难题有一个解释，但我们的项目将开始研究，寻求一个解释。

Pollination is important, ~70% of our food results directly from pollination as seeds, grains, fruits and berries. It is important to plants too for reproduction, which not only produces the next generation but creates variation upon which natural selection can act. This variation enables plants to adapt to changing environments and colonize new habitats. Most plants produce hermaphrodite flowers, but plants cannot move or actively choose a partner, instead they have evolved intriguing strategies to prevent self-pollination and promote cross-pollination. One of the most remarkable of these strategies is heterostyly, which uses insect pollinators (hetero=different; style=female structure). Charles Darwin observed that Primroses have two forms of flower, pin with a long style and short stamens, and thrum with a short style and longs stamens. These reciprocal positions facilitate pollen transfer by insect visitors between each flower type. A group of genes, known collectively as the S locus, controls development of the two forms of flower. A rich history of scientific research on Primroses by early botanists and geneticist made heterostyly an important textbook example of a plant breeding system. Our study will add to this work by using the latest research tools to explore how heterostyly arose, how it is controlled and why it occasionally goes wrong.We sequenced the Primrose (Primula vulgaris) genome and identified a group of five genes that control development of its two flower types. These genes are found only in thrum and are absent in pin plants. Only those individuals that inherit this gene cluster can produce thrum flowers. Our studies show the gene which we believe is responsible for elongating stamens in thrum flowers arose ~51.7million years ago in an ancestor of all modern Primula species. We have also identified the gene responsible for controlling style length. The gene cluster contains a further three genes and in this study we will characterize their function to determine how they work together to control the floral architectures of pin and thrum flowers that facilitate insect-mediated pollination in the Primrose. Over the past 51.7 million years, 30 different species of Primula have lost the ability to produce two types of flower, they all have long styles and long stamens and never produce short styled flowers. These homostyles (Homo = same) do not use insect pollinators, but self-fertilize. Our studies suggest the gene that controls style length has been lost or damaged in these species.These homostyle species provide an exciting opportunity to explore how one gene has, over time, on multiple separate occasions, been lost or damaged during the evolution of the different Primula species. This is important because understanding how development has gone wrong can help explain how it normally works. We will use our Primrose genome sequence to identify and characterize the corresponding S locus gene clusters in these different Primula species to discover the gene mutation that has resulted in the loss of heterostyly. Most plant and animal genes are present in two copies, one set from the mother, one from the father; this is useful, if one copy is damaged, the second copy acts as backup so function is retained, it also enables repair of the damaged copy using the other as a template. This arrangement provides genetic stability from generation to generation. One very surprising finding from our studies of genes controlling heterostyly in Primula is that they are present only as a single copy, there is no back up copy. It is therefore surprising that heterostyly is stable as any genetic damage to the key genes cannot be repaired. We do not yet have an explanation for this conundrum but our project will initiate studies to seek an explanation.