Comparative Genomics of Papaya Chromosomes

木瓜染色体的比较基因组学

• 批准号: 0421803
• 负责人: Ray Ming
• 金额: $ 289.69万
• 依托单位: Hawaii Agriculture Research Center
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-09-01 至 2006-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0421803&HistoricalAwards=false
• 关键词: Comparative; Genomics; Papaya; Chromosomes

Papaya (Carica papaya L.) is a principal fruit crop of tropical and subtropical regions worldwide. Papaya fruit is a major export commodity in Hawaii, and is also in production in Florida, the Rio Grande Valley of Texas, and southern California. Papaya trees are grown for both fruit and papain, a commercially valuable proteolytic enzyme. Papaya is one of the few plant species which fruit throughout the year and can produce ripe fruit in as little as nine months from planting. A papaya tree may live for 25 years or longer, bearing continuously with one or more fruit in each leaf axil.Papaya has male, female, and hermaphrodite sexes, with a primitive Y chromosome that provides a unique opportunity to study sex chromosome evolution and sex determination. Sex chromosomes in animals are ancient - about 300 million years old, and Y-chromosomes are genetically eroded. Flowering plants appeared about 130-200 million years ago and plant sex chromosomes evolved more recently. The Silene genus with its estimated 20 - 25 million-year ancestry has generally been thought to contain the most recently evolved XY system known in eukaryotes. Yet 90% of the Y chromosome in Silene is degenerated and suppressed for recombination. The recently discovered primitive Y chromosome in papaya has a small male specific region that comprises only about 10% of the Y chromosome. This male specific region (MSY) shows much more moderate degeneration and suppression of recombination. Thus the papaya system appears to be the most recently evolved XY system known to date, offering potential insights into the question of how evolution of the sex chromosome began. Unraveling plant sex determination processes will have direct applications in production of crop plants such as papaya, asparagus, spinach, black pepper, yam, and pistachio. This project seeks to explore the nature of incipient sex chromosomes. The papaya MSY and the corresponding X-specific region will be sequenced and characterized. To estimate the antiquity of the non-recombining region, the extent of divergence of X and Y gene pairs along the region will be calculated, giving special attention to candidate gene(s) for sex determination. Comparing the X and Y DNA sequences and their surroundings will reveal types and extent of chromosomal rearrangements and the role of transposable elements in the degeneration of MSY. The relative position of MSY to the centromere of the primitive Y chromosome will be clarified by pachytene and fiber Fluorescent In Situ Hybridization (FISH) analyses. It is expected that this project will generate candidate genes for sex determination and embryo lethality for the papaya research community.Access to project outcomesDNA sequence data and trace files will be deposited in GenBank, and project data made available at the websites of Hawaii Agriculture Research Center (http://www.hawaiiag.org/harc) and University of Georgia (http://www.plantgenome.uga.edu/). Bacterial Artificial Chromosome (BAC) clones will be distributed by the Plant Genome Mapping Laboratory at the University of Georgia and also deposited in a public BAC distribution center.

番木瓜（Carica papaya L.）是世界热带和亚热带地区的主要水果作物。木瓜是夏威夷的主要出口商品，佛罗里达、得克萨斯州的格兰德河谷和加州南部也有生产。种植木瓜树是为了水果和木瓜蛋白酶，一种商业上有价值的蛋白水解酶。木瓜是为数不多的一年四季都能结出果实的植物之一，从种植到成熟只需九个月。木瓜树可以活25年或更长时间，在每个叶腋连续结一个或多个果实。木瓜有雄性，雌性和雌雄同体的性别，具有原始的Y染色体，为研究性染色体进化和性别决定提供了独特的机会。动物的性染色体是古老的--大约3亿年前，Y染色体在基因上被侵蚀了。开花植物出现在大约1.3亿至2亿年前，植物性染色体的进化更近。蝇子草属估计有2000 - 2500万年的祖先，通常被认为含有真核生物中已知的最近进化的XY系统。然而，在蝇子草中，90%的Y染色体是退化的，并被抑制重组。最近在番木瓜中发现的原始Y染色体有一个小的雄性特异性区域，仅占Y染色体的10%左右。该雄性特异性区域（MSY）显示出更温和的变性和重组抑制。因此，木瓜系统似乎是迄今为止已知的最新进化的XY系统，为性染色体如何开始进化的问题提供了潜在的见解。 解开植物性别决定过程将直接应用于生产作物，如木瓜，芦笋，菠菜，黑胡椒，山药，和开心果。该项目旨在探索早期性染色体的性质。 将对番木瓜MSY和相应的X特异性区域进行测序和表征。为了估计非重组区域的古老性，将计算X和Y基因对沿着该区域的分歧程度，特别注意性别决定的候选基因。比较X和Y DNA序列及其周围环境将揭示染色体重排的类型和程度以及转座因子在MSY变性中的作用。MSY与原始Y染色体着丝粒的相对位置将通过粗线期和纤维荧光原位杂交（FISH）分析来阐明。预计该项目将为番木瓜研究界产生性别决定和胚胎致死的候选基因。项目结果的DNA序列数据和跟踪文件将保存在GenBank中，项目数据可在夏威夷农业研究中心（http：//www.hawaiiag.org/harc）和格鲁吉亚大学（http：//www.plantgenome.uga.edu/）的网站上获得。细菌人工染色体（BAC）克隆将由格鲁吉亚大学的植物基因组作图实验室分发，并存放在公共BAC分发中心。