Integration of chromosome synapsis and recombination by AtZYP1 during Arabidopsis meiosis

减数分裂在所有有性生殖的真核生物的生命周期中起着中心作用。了解这一过程对进一步研究生殖、生育、遗传和育种至关重要。减数分裂是细胞分裂的一种特殊形式，在此过程中，一轮DNA复制之后是两次细胞分裂，从而使染色体含量从二倍体减少到单倍体。同源染色体在第一次减数分裂时的准确分离依赖于同源染色体对（同源染色体）之间的物理连接的形成，称为交叉。交叉产生于减数分裂前期的同源重组，是遗传杂交的物理表现。在它们不存在的情况下，同系物在第二次减数分裂时姐妹染色单体分离后随机分离，形成非整倍体配子。近年来研究发现，减数分裂前期发生的染色体配对、突触和同源重组等关键事件是高度整合的。此外，越来越清楚的是，控制减数分裂重组的许多关键决定发生在早期前期I，即同源染色体突触启动时，从瘦素到合子蛋白的转变。突触是由突触复合体（SC）介导的，这是一种结构保守的三方蛋白复合体。SC于1956年被发现，随后在大多数真核生物中被发现。它由两个平行于同源染色体对长度的横向元素组成。它们相隔100纳米的距离，并通过横向细丝连接在一起，这些细丝交叉在一起，以“拉链状”的排列方式跨越中心区域。值得注意的是，SC的功能仍然是一个谜。然而，最近对出芽酵母和拟南芥的研究表明，染色体突触的启动与重组途径的控制之间存在密切联系。在本提案中，我们的目标是阐明拟南芥中这种关系的本质。我们最近分离了ZYP1，这是在高等植物中鉴定到的第一个SC蛋白。我们发现，在没有ZYP1的情况下，正常的重组受到干扰，导致非同源染色体之间发生不适当的重组事件。因此，在第一次减数分裂时精确的染色体分离是不可能的。在这个项目中，我们的目标是确定ZYP1蛋白如何阻止非同源重组。它是否直接与早期重组机制相互作用以确保重组相互作用的保真度？或者它可能影响早期I前期的染色体动力学，因为在减数分裂过程中，重组途径与染色体组织之间的密切关系越来越清楚。我们预计，这些研究将首次确定SC的功能超越了简单的结构作用，并提供进一步的证据，证明驱动重组的生化过程与染色体动力学密切协调

Meiosis occupies a central role in the life cycles of all sexually reproducing eukaryotes. An understanding of this process is critical to furthering research on reproduction, fertility, genetics and breeding. Meiosis is a specialized form of cell-division during which a single round of DNA replication is followed by two cell-divisions thereby reducing the chromosome content from diploid to haploid. Accurate segregation of homologous chromosomes at the first meiotic division is dependent on the formation of physical connections, known as chiasmata, between homologous chromosome pairs (homologues). Chiasmata arise from homologous recombination during prophase I of meiosis and are the physical manifestation of genetic crossovers. In their absence the homologues segregate at random leading to the formation of aneuploid gametes following the separation of the sister chromatids at the second meiotic division. In the past few years it has emerged that the key events of meiosis, chromosome pairing and synapsis and homologous recombination that occur during prophase I of meiosis are highly integrated. Also, it is increasingly clear that many of the key decisions in the control of meiotic recombination occur in early prophase I at the time of the transition from leptotene to zygotene when homologous chromosome synapsis is initiated. Synapsis is mediated by the synaptonemal complex (SC), a structurally conserved, tripartite proteinaceous complex. The SC was discovered in 1956 and has subsequently been found in the majority of eukaryotes. It is comprised of two lateral elements running in parallel the length of the homologous chromosome pairs. These are separated by a distance of 100nm and are linked by transverse filaments that interdigitate to span the central region in a 'zipper-like' arrangement. Remarkably, the function of the SC remains a mystery. However, recent studies in budding yeast and our own in Arabidopsis point to a strong link between initiation of chromosome synapsis and the control of the recombination pathway. In this proposal it is our objective to elucidate the nature of this relationship in Arabidopsis. We have recently isolated ZYP1 the first SC protein to be identified in higher plants. It encodes the transverse filament of the SC. We have discovered that in the absence of ZYP1 normal recombination is perturbed such that inappropriate recombination events occur between non-homologous chromosomes. Hence accurate chromosome segregation at the first meiotic division is impossible. In this project we aim to establish how the ZYP1 protein prevents non-homologous recombination. Does it directly interact with the early recombination machinery to ensure the fidelity of recombination interactions? Or perhaps it affects chromosome dynamics in early prophase I, since is increasingly clear that there is a close relationship between the recombination pathway and chromosome organization throughout meiosis. We anticipate that these studies will establish for the first time a SC function beyond a simple structural role and provide further evidence that the biochemical processes that drive recombination are closely co-ordinated by chromosome dynamics