Syntenic relationships between cucumber (Cucumis sativus L.) and melon (C. melo L.) chromosomes as revealed by comparative genetic mapping
1 Horticulture College, Northwest A & F University, Yangling 712100, China
2 Horticulture Department, University of Wisconsin, Madison, WI 53706, USA
3 USDA ARS Tropical Agriculture Research Station, Mayaguez, P.R. 00680, Puerto Rico
4 IRTA, Center for Research in Agricultural Genomics CSIC-IRTA-UAB, Campus UAB, Edifici CRAG, 08193 Bellaterra (Barcelona), Spain
5 USDA ARS Vegetable Crops Research Unit, Horticulture Department, University of Wisconsin, Madison, WI 53706, USA
6 USDA-ARS, Forage & Range Research Laboratory, Utah State University, Logan, UT 84322 USA
7 Horticulture College, Northeast Agricultural University, Harbin, 150030, China
8 Department of Biology, West Virginia State University Institute, WV 25112, USA
9 Vegetable Research Institute, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China
BMC Genomics 2011, 12:396 doi:10.1186/1471-2164-12-396Published: 5 August 2011
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 F2- 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.