Genetic and physical maps around the sex-determining M-locus of the dioecious plant asparagus
Genetic and physical maps around the sex-determining M-locus of the dioecious plant asparagus
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DOI：
10.1007/s00438-007-0235-z
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发表时间：
2007-09-01
影响因子：
3.1
通讯作者：
Jung, Christian
中科院分区：
文献类型：
--
作者：
Telgmann-Rauber, Alexa;Jamsari, Ari;Jung, Christian
芦笋是雌雄异株植物。位于一对同形性染色体上的一个称为M基因座的区域控制着芦笋的两性异形。这项工作的目的是从基因组中的位置克隆芦笋中决定性别的区域。应调查的结构，包括M的区域，并与其他雌雄异株模式物种的性别决定区。为了建立一个改进的基础物理作图，高分辨率的遗传图谱丰富的AFLP标记紧密连锁的目标基因座进行散装分离分析。通过用AFLP和STS标记筛选BAC文库，然后进行染色体步移，可以建立具有8个重叠群的物理图谱。然而，重叠群之间的缺口由于过多的重复元件而不能闭合。令人惊讶的是，M基因座一侧的两个重叠群没有重叠，尽管它们已经用两个标记建立，这两个标记定位在性基因座侧翼低至0.25 cM的距离。因此，标记的聚集表明M区内重组频率降低。在M基因座的相对侧，重叠群以0.38 cM的距离作图。对4个紧密连锁的BAC克隆进行了部分测序，鉴定出64个推定的ORF。有趣的是，只有25%的ORF与已知蛋白质和EST序列相似。此外，芦笋性别决定区的重复序列的积累和低的基因密度被揭示。分子细胞遗传学和序列分析的BAC侧翼的M-位点表明，BAC含有高度重复的序列，定位于所有芦笋染色体上的着丝粒和近着丝粒的位置，这阻碍了本地化的M-位点的单对性染色体。我们推测雌雄异株的蝇子草、番木瓜和芦笋可能代表了XX，XY性别决定系统进化的三个阶段。鉴于芦笋仍然很少产生两性花，并具有同形性染色体，该物种可能是一个理想的系统，以进一步研究早期性染色体进化和diophyll的起源。
Asparagus officinalis L. is a dioecious plant. A region called the M-locus located on a pair of homomorphic sex chromosomes controls the sexual dimorphism in asparagus. The aim of this work was to clone the region determining sex in asparagus from its position in the genome. The structure of the region encompassing M should be investigated and compared to the sex-determining regions in other dioecious model species. To establish an improved basis for physical mapping, a high-resolution genetic map was enriched with AFLP markers closely linked to the target locus by carrying out a bulked segregant analysis. By screening a BAC library with AFLP- and STS-markers followed by chromosome walking, a physical map with eight contigs could be established. However, the gaps between the contigs could not be closed due to a plethora of repetitive elements. Surprisingly, two of the contigs on one side of the M-locus did not overlap although they have been established with two markers, which mapped in a distance as low as 0.25 cM flanking the sex locus. Thus, the clustering of the markers indicates a reduced recombination frequency within the M-region. On the opposite side of the M-locus, a contig was mapped in a distance of 0.38 cM. Four closely linked BAC clones were partially sequenced and 64 putative ORFs were identified. Interestingly, only 25% of the ORFs showed sequence similarity to known proteins and ESTs. In addition, an accumulation of repetitive sequences and a low gene density was revealed in the sex-determining region of asparagus. Molecular cytogenetic and sequence analysis of BACs flanking the M-locus indicate that the BACs contain highly repetitive sequences that localize to centromeric and pericentromeric locations on all asparagus chromosomes, which hindered the localization of the M-locus to the single pair of sex chromosomes. We speculate that dioecious Silene, papaya and Asparagus species may represent three stages in the evolution of XX, XY sex determination systems. Given that asparagus still rarely produces hermaphroditic flowers and has homomorphic sex chromosomes, this species may be an ideal system to further investigates early sex chromosome evolution and the origins of dioecy.