Telomere Hypervariability in the Fungus, Magnaporthe Oryzae - A Model Plant Pathogen

真菌中的端粒高度变异，稻瘟病菌 - 一种模型植物病原体

• 批准号: 0653930
• 负责人: Mark Farman
• 金额: $ 33.59万
• 依托单位: University of Kentucky Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-04-01 至 2012-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0653930&HistoricalAwards=false
• 关键词: Telomere; Hypervariability; Fungus; Magnaporthe; Oryzae

Telomeres are specialized DNA sequences that form the ends of eukaryotic chromosomes and are required to prevent the progressive loss of terminal DNA sequences during chromosome replication. In most eukaryotes, the telomeres consist of tandem arrays of simple sequence repeats; and the end-maintenance problem is solved by the periodic addition of new repeats to existing ends by telomerase, a specialized reverse transcriptase. Some eukaryotes lack telomerase and have different strategies for solving the end replication problem. The best studied example is Drosophila, whose telomeres consist of the retrotransposons TART and HeT A, which also are added to chromosome ends via reverse transcription. In addition to protecting chromosome ends, telomeres are involved in chromosome pairing and movement, can silence neighboring genes and are highly plastic. This laboratory is studying telomere plasticity in the plant pathogenic fungus Magnaporthe oryzae, as this has been associated with pathogenic variability. M. oryzae isolates that infect perennial ryegrass have unusually unstable telomeres that undergo continual rearrangements both in culture and in planta. By comparison, telomeres in most other host specific forms of this fungus are quite stable. Sequencing revealed that the chromosome ends of the ryegrass pathogens are organized very differently from those in a strain with stable telomeres. Specifically, the ryegrass pathogen telomeres contain tandem arrays of retrotransposon-like sequences separated by short TTAGGG motifs. The arrays are capped at the chromosome end by a "normal" telomere sequence, which in M. oryzae is (TTAGGG)n. This arrangement is reminiscent of the TRAS and SART retrotransposons, which insert into telomeres in the silkworm, Bombyx mori. However, the M. oryzae elements, which we call MoTERs (for M. oryzae telomere-exclusive repeats), are organized quite differently to TRAS and SART. Most importantly, they lack the endonuclease gene required for insertion into DNA. Instead, the particular organization of MoTERs at the chromosome ends suggests they are added on to the ends of chromosomes in the same manner as TART and HeT A in Drosophila. These observations lead to the hypothesis that telomere instability in M. oryzae is due to the activities of two telomere maintenance mechanisms - one utilizing telomerase to extend TTAGGG repeats, and the other involving retrotransposition of MoTERs sequences onto free DNA ends that result from end degradation. The goal of the experiments is to test this hypothesis and develop resources for future mechanistic studies. The specific aims are: 1) To determine the molecular basis for telomere instability, and 2) To study the genetics of MoTER transposition.Intellectual merit: The experiments are an important first step in the characterization of a highly novel system of telomere maintenance in a well-developed experimental model. It will provide important insight into factors affecting telomere stability and the dynamics of telomere maintenance. In addition, this study will open the door to future investigations into poorly understood areas, such as mechanisms and regulation of terminal transposition, the evolutionary relationship between the two telomere maintenance strategies, and the influence of telomere dynamics on neighboring gene expression.Broader impacts: This project will provide a stimulating research experience for a postdoctoral scholar and an undergraduate student. In addition, an undergraduate independent research project will be offered each summer. Minority student involvement in the project will be fostered through links with the Kentucky Young Scientist Summer research program. The Postdoc will attend workshops for computer skills, etc. and are strongly encouraged to attend the various professional development workshops offered on the UK campus, to help them become better prepared for their future careers.

端粒是形成真核生物染色体末端的特化DNA序列，并且在染色体复制期间需要防止末端DNA序列的进行性丢失。在大多数真核生物中，端粒由简单重复序列的串联阵列组成;而末端维持问题是通过端粒酶（一种专门的逆转录酶）定期向现有末端添加新的重复序列来解决的。一些真核生物缺乏端粒酶，并有不同的策略来解决末端复制问题。 研究得最好的例子是果蝇，其端粒由反转录转座子TART和HeTA组成，它们也通过反转录添加到染色体末端。 除了保护染色体末端，端粒还参与染色体配对和运动，可以沉默邻近基因，并且具有高度可塑性。 该实验室正在研究植物病原真菌Magnaporthe pigmentosa中的端粒可塑性，因为这与病原变异性有关。M.感染多年生黑麦草的分离株具有不稳定的端粒，在培养物和植物中都经历了连续的重排。相比之下，这种真菌的大多数其他宿主特异性形式的端粒相当稳定。测序显示，黑麦草病原体的染色体末端的组织与具有稳定端粒的菌株中的染色体末端的组织非常不同。具体而言，黑麦草病原体端粒含有由短TTAGGG基序分隔的逆转录转座子样序列的串联阵列。 这些阵列在染色体末端被一个“正常”的端粒序列覆盖，在M。（TTAGGG）;这种排列让人想起TRAS和SART反转录转座子，它们插入家蚕的端粒中。 然而，M.我们称之为MoTER（M.端粒排他性重复序列）的组织方式与TRAS和SART完全不同。 最重要的是，它们缺乏插入DNA所需的核酸内切酶基因。 相反，MoTER在染色体末端的特殊组织表明它们以与果蝇中的TART和HeT A相同的方式添加到染色体末端。 这些观察结果导致了一种假说，即M.这是由于两种端粒维持机制的活性-一种利用端粒酶来延长TTAGGG重复，另一种涉及将MoTER序列反转录转座到由末端降解产生的游离DNA末端上。 实验的目的是验证这一假设，并为未来的机制研究开发资源。 具体目标是：1）确定端粒不稳定的分子基础; 2）研究MOTER转座的遗传学。智力价值：这些实验是在一个成熟的实验模型中表征一个高度新颖的端粒维持系统的重要的第一步。 它将提供重要的洞察因素影响端粒的稳定性和动态端粒维护。此外，这项研究将打开大门，未来的调查知之甚少的领域，如机制和调控终端转座，两个端粒维护策略之间的进化关系，以及端粒动态对邻近基因表达的影响。更广泛的影响：该项目将提供一个激励的研究经验，为博士后学者和本科生。此外，每年夏天将提供一个本科生独立研究项目。少数民族学生参与该项目将通过与肯塔基州青年科学家夏季研究计划的联系来促进。 博士后将参加计算机技能研讨会等，并强烈鼓励参加英国校园提供的各种专业发展研讨会，以帮助他们为未来的职业生涯做好更好的准备。