The roles of DNA ligases in novel plant recombination pathways: from DNA repair to gene targeting.

DNA对生长和繁殖至关重要。它包含从一代传递到下一代的遗传信息，并编码细胞生存和分裂所需的因子。然而，细胞中的DNA不断受到细胞内产生的反应分子的攻击，或由环境因素引起，包括致癌物，UVB和土壤污染物，如重金属。DNA损伤可能对生物体产生严重的影响;如果没有准确修复，单个DNA双链断裂足以导致细胞死亡。因此，所有生物体都需要有效的DNA修复机制来抵消这种损伤。几乎所有DNA修复途径中的一个重要步骤是DNA末端的重新连接，这是由DNA连接酶催化的。虽然酵母有两个基因，但包括哺乳动物和植物在内的高等生物有三个DNA连接酶基因，在DNA复制和修复过程中维持基因组的专门作用。在这项研究中，我们将确定不同的DNA连接酶在高等植物拟南芥中的作用。具体来说，我们确定了每个DNA连接酶的运作途径，以及在不利条件下植物生长的重要性。作为这项分析的一部分，我们将探讨每个DNA连接酶在重组中的作用-两个DNA分子连接形成一个新分子的过程。在DNA修复中，重组可以通过两个过程发生;一种修复方法使用受损DNA的完整拷贝作为修复模板。这个过程被称为同源重组，它涉及相似（同源）序列的连接（重组）。第二个过程在很大程度上与DNA序列无关，称为非同源末端连接。重要的是，我们要了解植物中的重组过程，因为在不利的环境胁迫条件下，需要DNA修复才能使作物生长，这些途径的失败将导致作物产量降低和有害突变在后代中的积累。考虑到气候变化对英国作物生产力的影响，现在我们了解植物如何应对环境压力尤为重要。了解植物中的重组对于培育作物新品种也很重要。DNA修复途径的操纵将有助于开发出能够耐受变化的气候条件的作物，最近的研究还表明植物适应中的同源重组可以增强对病原体的耐受性。此外，改变植物重组途径的活性将对我们如何制造转基因植物产生影响。转基因通常整合在植物DNA的随机位置。然而，高水平的同源重组将使我们能够将转基因靶向基因组中的特定位置，从而实现更可靠的表达，并为植物中天然存在的“微调”基因开辟了可能性。这将导致第二代转基因植物的出现，从而解决对当前方法的许多批评。

DNA is essential for growth and reproduction. It contains the genetic information that is passed from one generation to the next, and encodes the factors needed for a cell to survive and divide. However, DNA in the cell is under constant attack from reactive molecules generated from within the cell or caused by environmental factors including carcinogens, UVB and soil pollutants such as heavy metals. DNA damage can have severe repercussions for the organism; a single DNA double strand break is sufficient to cause cell death if not accurately repaired. All organisms therefore require effective DNA repair mechanisms to counteract this damage. An essential step in nearly all DNA repair pathways is the re-joining of DNA ends, which is catalysed by a DNA ligase enzyme. Whilst yeast has two genes, higher organisms including mammals and plants have three DNA ligase genes, with specialised roles in maintaining the genome during DNA replication and repair. In this study we will determine the roles of the different DNA ligases in the higher plant Arabidopsis thaliana. Specifically, we determine the pathways in which each DNA ligase operates, and the importance for plant growth in adverse conditions. As part of this analysis we will characterise the role of each DNA ligase in recombination - the process whereby two DNA molecules are joined to make a new molecule. In DNA repair, recombination can occur by two processes; one method of repair uses an intact copy of the damaged DNA as a template for repair. This process is termed homologous recombination, and it involves the joining (recombining) of similar (homologous) sequences. The second process is largely independent of DNA sequence and is termed non-homologous end joining. It is important that we understand recombination processes in plants because DNA repair is required to allow growth of crop plants under conditions of adverse environmental stress, and failure of these pathways will both result in reduced crop yields and the accumulation of deleterious mutations in future generations. Given concerns over the impact of climate change on UK crop productivity, on it is now particularly important now that we understand how plants respond to environmental stresses. Understanding recombination in plants is also important for breeding new varieties of crop plants. Manipulation of DNA repair pathways will help develop crops that will tolerate altered climatic conditions and recent studies have also implicated homologous recombination in plant adaptation to give greater tolerances to pathogens. In addition, changing the activities of the plant recombination pathways will have effects on how we make transgenic plants. Transgenes usually integrate at random locations in the plant DNA. However, high levels of homologous recombination would allow us to target a transgene to a specific location in the genome, enabling more reliable expression and opening up the possibility of 'fine tuning' genes that are found naturally in the plant. This would lead to a second generation of transgenic plants that would address many of the criticisms of current methodologies.