Horticulture College, Northwest A & F University, Yangling 712100, China.
BMC Genomics. 2011 Aug 5;12:396. doi: 10.1186/1471-2164-12-396.
Cucumber, Cucumis sativus L. (2n = 2 × = 14) and melon, C. melo L. (2n = 2 × = 24) are two important vegetable species in the genus Cucumis (family Cucurbitaceae). Both species have an Asian origin that diverged approximately nine million years ago. Cucumber is believed to have evolved from melon through chromosome fusion, but the details of this process are largely unknown. In this study, comparative genetic mapping between cucumber and melon was conducted to examine syntenic relationships of their chromosomes.
Using two melon mapping populations, 154 and 127 cucumber SSR markers were added onto previously reported F(2)- and RIL-based genetic maps, respectively. A consensus melon linkage map was developed through map integration, which contained 401 co-dominant markers in 12 linkage groups including 199 markers derived from the cucumber genome. Syntenic relationships between melon and cucumber chromosomes were inferred based on associations between markers on the consensus melon map and cucumber draft genome scaffolds. It was determined that cucumber Chromosome 7 was syntenic to melon Chromosome I. Cucumber Chromosomes 2 and 6 each contained genomic regions that were syntenic with melon chromosomes III+V+XI and III+VIII+XI, respectively. Likewise, cucumber Chromosomes 1, 3, 4, and 5 each was syntenic with genomic regions of two melon chromosomes previously designated as II+XII, IV+VI, VII+VIII, and IX+X, respectively. However, the marker orders in several syntenic blocks on these consensus linkage maps were not co-linear suggesting that more complicated structural changes beyond simple chromosome fusion events have occurred during the evolution of cucumber.
Comparative mapping conducted herein supported the hypothesis that cucumber chromosomes may be the result of chromosome fusion from a 24-chromosome progenitor species. Except for a possible inversion, cucumber Chromosome 7 has largely remained intact in the past nine million years since its divergence from melon. Meanwhile, many structural changes may have occurred during the evolution of the remaining six cucumber chromosomes. Further characterization of the genomic nature of Cucumis species closely related to cucumber and melon might provide a better understanding of the evolutionary history leading to modern cucumber.
黄瓜（Cucumis sativus L.）和甜瓜（C. melo L.）分别是葫芦科黄瓜属和甜瓜属的两种重要蔬菜作物。两种作物均起源于亚洲，大约在 900 万年前发生分化。黄瓜被认为是由甜瓜通过染色体融合进化而来，但这一过程的细节尚不清楚。本研究通过比较黄瓜和甜瓜的遗传图谱，研究了它们染色体之间的同线性关系。
利用两个甜瓜作图群体，分别将 154 个和 127 个黄瓜 SSR 标记添加到之前报道的基于 F2 和 RIL 的遗传图谱上。通过图谱整合构建了一个共识甜瓜连锁图谱，该图谱包含 401 个共显性标记，分布在 12 个连锁群中，其中 199 个标记来源于黄瓜基因组。根据共识甜瓜图谱上的标记与黄瓜草图基因组支架之间的关联，推断出甜瓜和黄瓜染色体之间的同线性关系。结果表明，黄瓜第 7 号染色体与甜瓜第 1 号染色体同源。黄瓜第 2 号和第 6 号染色体分别与甜瓜第 3+5+11 号和第 3+8+11 号染色体的基因组区域同源。同样，黄瓜第 1、3、4 和 5 号染色体分别与之前被指定为第 2+12、第 4+6、第 7+8 和第 9+10 号染色体的两个甜瓜染色体的基因组区域同源。然而，这些共识连锁图谱上几个同线性块中的标记顺序并不一致，这表明在黄瓜的进化过程中，发生了比简单染色体融合更为复杂的结构变化。
本研究进行的比较作图支持了这样一种假设，即黄瓜染色体可能是由一个 24 条染色体的祖先物种通过染色体融合形成的。除了可能发生倒位外，自与甜瓜分化以来的 900 万年里，黄瓜第 7 号染色体基本保持完整。与此同时，在剩余 6 条黄瓜染色体的进化过程中，可能发生了许多结构变化。进一步对与黄瓜和甜瓜关系密切的黄瓜属物种的基因组特性进行表征，可能有助于更好地了解导致现代黄瓜产生的进化历史。
