杨梅雌雄性别决定的遗传和基因组学基础

Chinese bayberry (Myrica rubra ) is a subtropical evergreen fruit tree widely distributed in southern China.　The rapid industry development requires novel varieties to meet the environmental changes, cultivation methods and market demand for higher fruit quality. Bayberry trees are generally dioecious, with female plants cultivated for fruit. The genetic mechanism controlling the sex traits has not been solved, which in part hamper the cross breeding program. This research will use polymorphic and co-dominant SSR markers derived from both genome and transcript sequences to screen the male and female populations to identify markers linked to sex traits. By employing comparative transcriptomes and miRNA of male and female flower, some candidate genes related to sex determination will be found and more SSR marker can be developed. A reference molecular marker linkage map based on 'Biqi' x 'Dongkui' would serve as genetic analysis tool to locate the genomic region for sex determination and its interaction mode based on segregation populations. A number of closely linked markers to sex traits can be inferred. This research will provide fundamental basis for the sex determination in genetics and genomics, which certainly are helpful for cross breeding and selection of Chinese bayberry.

杨梅是我国南方重要的特色亚热带果树，产业的迅速发展迫切需求适应新环境、栽培模式和消费市场的高品质新品种。杨梅为雌雄异株，栽培品种绝大多数为雌株，雄株仅提供授粉。目前对于杨梅的性别决定遗传因子尚不清楚，限制了现代杂交育种工作的开展。本项目将应用前期研究积累的杨梅栽培品种（雌株）和雄株资源，采用多态性共显性基因组和转录组开发的SSR分子标记评价雌雄群体遗传结构，分析与性别关联的分子标记。通过比较雌雄花组织转录组和miRNA，分析与性别分化相关的候选基因和序列差异，开发新的SSR标记。利用荸荠x东魁杂交群体构建杨梅高密度分子标记连锁图谱，分析杨梅雌、雄性别控制遗传模式和关联基因组结构特征。找出与性别分化相关基因组区段和相关的分子标记。 本研究将解决杨梅遗传、基因组、育种研究急需分子标记连锁图谱问题，在此基础上解析杨梅雌雄性别决定遗传和基因组学机制，对杨梅杂交育种有重要理论指导意义。

杨梅是我国南方重要的特色亚热带果树，产业的迅速发展迫切需求适应新环境、栽培模式和消费市场的高品质新品种。杨梅为雌雄异株，栽培品种绝大多数为雌株，雄株仅提供授粉。目前对于杨梅的性别决定遗传因子尚不清楚，限制了现代杂交育种工作的开展。本研究构建了第一个杨梅杂交群体 ‘荸荠’x ‘东魁’，实现品种间杂交，获得可靠的后代。应用前期开发的基因组SSR标记构建骨干型连锁图谱，包含标记数量118个,长度508cM。用这些上图的标记评价雌雄100多个品系群体，初步筛选出10个SSR标记与性别群体关联。其中第8连锁群上有5个，覆盖80%的染色体区域。应用RAD-seq技术开发了8525个SNP标记，构建了高密度连锁图谱，包含3075个SNPs, 长度531cM, 407个单倍型区块。这些SNP以及SSR标记是组装基因组到染色体水平的依据。我们组装了高质量的杨梅雌、雄基因组，其大小约为313 Mb，90%的组装序列可以锚定到8条连锁群上。杨梅基因组共预测到32,493个基因。通过对雌、雄混池进行BSA测序，并将测序得到的read比对到雌、雄参考基因组中，找出59 Kb的雌特异区域并将其定位到第8连锁群的末梢，该区域包含大量的转座子序列和7个基因，其中4个基因与花发育相关。该59 Kb的雌特异区域可能来源于同源区域的复制和重排，且为非重组区域。基于雌特异基因及其同源基因开发的性别特异标记在不同地理来源的雌、雄杨梅材料上验证均与性别类型分离一致，准确度100%。基于雌特异的区域推测杨梅性别决定机制为ZW型，即雌株为杂合子。杨梅基因组测序为植物性染色体进化、分子生物学、遗传与现代育种的研究奠定基础。