The evolution of dimorphic sex chromosomes in the genus Coccinia (Cucurbitaceae)

很少陆地植物有专门的雄性和雌性（雌雄异株）孢子体。尽管总体上取得了有限的成功，但植物的雌雄同体已经进化了许多次，这意味着各种形式的性别决定的独立进化，包括XY性别决定、同态性染色体和异型性染色体。后者是已知的大麻，Humulus, Silene， Rumex和Coccinia，葫芦科，这是本提案的重点。所有c. 29种球虫都是雌雄异株，但染色体只在c. grandis中被研究过，其中Y染色体比x长约2.5倍。是什么导致了如此长的Y染色体？球虫的核型进化途径是什么？关于第一个问题，正在测试的假设是，重复元素的积累导致了Y延伸，这将通过使用代表性差异分析和染色体行走来测试，并同时使用限制性内切酶进行消化。我们将通过生成球虫的系统发育和重建尽可能多的物种的核型进化来解决第二个问题（目前活着的收集：6种）。我们还将使用流式细胞术检查性别特异性C值，代表总核DNA含量。这对Silene的干叶进行了性别鉴定，并可能使我们推断球虫属植物标本室材料中存在异体。

Few land plants have specialized male and female (dioecious) sporophytes. In spite of this limited overall success, unisexuality in plants has evolved many times, implying the independent evolution of various forms of sex determination, including XY sex determination, homomorphic sex chromosomes, and heteromorphic sex chromosomes. The latter are known from Cannabis, Humulus, Silene, Rumex, and Coccinia, the Cucurbitaceae that is the focus of this proposal. All c. 29 species of Coccinia are dioecious, but chromosomes have only been studied in C. grandis, in which the Y chromosome is about 2.5 times longer than the X. We propose to investigate two questions; what led to the great length of the Y chromosome and what was the pathway of karyotype evolution in Coccinia? The hypothesis being tested in regard to the first question is that an accumulation of repetitive elements has led to Y elongation, which will be tested by using representational difference analysis and chromosome walking, and in parallel a digestion with restriction enzymes. We shall address the second question by generating a phylogeny for Coccinia and reconstructing the evolution of the karyotypes of as many species as possible (current living collection: six species). We will also use flow cytometry to check for sex-specific C values, representing the total nuclear DNA content. This has worked for sexing dried leaves in Silene and may allow us to infer the presence of heterosomes in herbarium material of Coccinia.