Inter-genomic conflict in gynodioecy and its effects on molecular evolution of mitochondrial genomes

在物种内部，变异是生物多样性的一个极其重要的组成部分，使种群能够适应环境的变化。这往往与环境变化（如南北差异）或当地环境（如生长在铅矿和铜矿上的耐金属植物，而同一物种的其他植物则没有这种耐受性）有关。在这里，我们计划研究一个由自然选择维持的变异案例，自然选择通过单一植物物种或种群中两种不同性别形式的利益和成本来发挥作用-雌雄同体（具有雌性和雄性功能，大多数植物的情况）和雌性（或雄性不育）。在少数的开花植物中，雌性和雌雄同体同时存在。这就是所谓的gynodioplasty。维持性别形式的进化过程可以在具有雄性不育植物的自然种群中进行最好的研究，例如车前草属（Plantago）的许多物种。车前属植物是野生草地的重要组成部分，易于利用。它们的遗传学研究相当深入，在几个物种中发现了雄性不育，使它们成为理想的研究生物。雌性被广泛用于植物育种，特别是在玉米等作物中，育种者希望产生杂交种，也可以防止花粉从转基因作物中“逃逸”。关于植物雌性（雄性不育）的遗传有很多信息。雄性不育通常是由植物线粒体DNA突变引起的（线粒体是动物和植物细胞细胞质中的微小结构，对能量产生至关重要）。这就是所谓的细胞质雄性不育。细胞质雄性不育是“自私遗传因素”的典型例子。一个物种获得了一个看似有害的突变，导致雄性不育，或雌性，尽管与雌雄同体相比，由于男性生育能力的丧失而处于劣势。这是因为作为雌性有一些优势--只要有来自雌雄同体的花粉，雌性通常可以比雌雄同体产生更多的种子，因为，通过“自私地”依赖他人使种子受精，它们有更多的资源可用于种子生产。它们的后代通常也有更高的存活率，因为雌性总是与不同的个体交配（雌雄同体通常通过自花受精繁殖，这些后代通常具有低存活率或生育力，称为“近亲繁殖衰退”）。有时，不育和非不育变种都可以保留在一个群体中，雌雄同体和雌性植物可以共存很长一段时间，物种内的线粒体DNA变异。然而，细胞核DNA的突变可以恢复失去的雌性功能，即使线粒体发生突变，也会导致两性畸形。因此，核基因和线粒体基因之间存在冲突，就像流感流行病一样，一种新的病毒通过突变出现，对它的抵抗力在人群中建立起来，直到一种不同类型的新病毒爆发（在这种情况下，宿主的抵抗力是由于免疫系统的变化，而不是抵抗突变在宿主人群中传播）。在雄性不育的情况下，核恢复突变有时可以在植物种群中传播，使植物再次成为雌雄同体。不育线粒体类型的优势，上面解释的原因，这种类型，然后是唯一剩下的。如果一个新的雄性不育突变后来侵入物种，这个过程可以重复。另一个有趣的事实是，车前草的线粒体DNA进化速度比大多数其他植物快数千倍，我们还将研究这种快速进化与不同性别类型之间的可能联系。该项目的结果将增加我们对维持雄性不育所涉及的过程的理解。

Within species variation is an extremely important component of biodiversity to allow populations to adapt to changes in their environment. This is often related to environmental variation (e.g. north-south differences) or local environments (e.g. metal-tolerant plants growing on lead and copper mines, whereas others of the same species have no such tolerance). Here, we plan to study a case of variation that is maintained by natural selection acting through the benefits and costs of two different sex forms in a single plant species or population - hermaphrodites (which have both female and male functions, the situation in most plants) and females (or male steriles). In a few percent of flowering plants, both females and hermaphrodites co-occur. This is called gynodioecy. The evolutionary processes involved in the maintenance of the sex forms can best be studied in natural populations with male sterile plants, such as many species in the genus Plantago (plantains). Plantago species are important components of wild grasslands, and easy to work with. Their genetics is quite well studied, and male steriles have been found in several species, making them the ideal study organisms.Females are widely used in plant breeding, particularly in crops like maize where breeders want to produce hybrids, and also to prevent the 'escape' of pollen from genetically modified crops. There is thus much information about the inheritance of femaleness (male sterility) in plants. Male sterility is often caused by a mutation in the mitochondrial DNA of the plant (mitochondria are tiny structures in the cytoplasm of animal and plant cells that are essential for energy generation). This is called cytoplasmic male-sterility. Cytoplasmic male sterility is a classic example of a 'selfish genetic element'. A species acquires a seemingly harmful mutation causing male sterility, or femaleness, despite the disadvantage compared to hermaphrodites due to loss of male fertility. This occurs because there are some advantages to being female - provided that pollen from hermaphrodites is available, females can often produce more seeds than the hermaphrodites, because, by 'selfishly' relying on others to fertilise their seeds, they have more resources available for seed production. Their offspring also often have higher survival, because females always mate with a different individual (hermaphrodites often reproduce by self-fertilisation and these progeny often have low survival or fertility, called 'inbreeding depression'). Sometimes the sterility and non-sterility variants can both remain in a population, and hermaphrodite and female plants may coexist for a long time, with mitochondrial DNA variation within the species. However, mutations in the nuclear DNA can restore the lost female function, leading to hermaphroditism even when the mitochondria are mutant. There is thus a conflict between nuclear and mitochondrial genes, rather like that in an influenza epidemic, where a new virus appears through mutation, and resistance against it builds up in the population until a new virus outbreak, of a different type, occurs (in this situation, the host's resistance is due to immune system changes, not to resistance mutations spreading in the host population). In the case of male sterility, a nuclear restorer mutation can sometimes spread in a plant population, making the plants mostly hermaphrodite again. The sterility mitochondrial type's advantages explained above cause this type to then be the only one remaining. If a new male sterility mutation later invades the species, the process can be repeated. Another interesting fact is that the mitochondrial DNA of Plantago evolves thousands of times faster than in most other plants, and we will also investigate a possible connection between this fast evolution and the different sex types. The results of the project will increase our understanding of the processes involved in the maintenance of male sterility.