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BMC Genomics. 2009; 10: 102.
Published online Mar 10, 2009. doi:  10.1186/1471-2164-10-102
PMCID: PMC2661093
A gene-rich linkage map in the dioecious species Actinidia chinensis (kiwifruit) reveals putative X/Y sex-determining chromosomes
Lena G Fraser,corresponding author1 Gianna K Tsang,1 Paul M Datson,1 H Nihal De Silva,1 Catherine F Harvey,1 Geoffrey P Gill,1,2 Ross N Crowhurst,1 and Mark A McNeilage1
1The New Zealand Institute for Plant and Food Research Limited, Auckland 1142, New Zealand
2ViaLactia Biosciences (NZ) Ltd, Auckland 1031, New Zealand
corresponding authorCorresponding author.
Lena G Fraser: lfraser/at/hortresearch.co.nz; Gianna K Tsang: gtsang/at/hortresearch.co.nz; Paul M Datson: pdatson/at/hortresearch.co.nz; H Nihal De Silva: ndesilva/at/hortresearch.co.nz; Catherine F Harvey: brutrix/at/xtra.co.nz; Geoffrey P Gill: geoff.gill/at/vialactia.com; Ross N Crowhurst: rcrowhurst/at/hortresearch.co.nz; Mark A McNeilage: mmcneilage/at/hortresearch.co.nz
Received September 19, 2008; Accepted March 10, 2009.
Abstract
Background
The genus Actinidia (kiwifruit) consists of woody, scrambling vines, native to China, and only recently propagated as a commercial crop. All species described are dioecious, but the genetic mechanism for sex-determination is unknown, as is the genetic basis for many of the cluster of characteristics making up the unique fruit. It is, however, an important crop in the New Zealand economy, and a classical breeding program would benefit greatly by knowledge of the trait alleles carried by both female and male parents. The application of marker assisted selection (MAS) in seedling populations would also aid the accurate and efficient development of novel fruit types for the market.
Results
Gene-rich female, male and consensus linkage maps of the diploid species A. chinensis have been constructed with 644 microsatellite markers. The maps consist of twenty-nine linkage groups corresponding to the haploid number n = 29. We found that sex-linked sequence characterized amplified region (SCAR) markers and the 'Flower-sex' phenotype consistently mapped to a single linkage group, in a subtelomeric region, in a section of inconsistent marker order. The region also contained markers of expressed genes, some of unknown function. Recombination, assessed by allelic distribution and marker order stability, was, in the remainder of the linkage group, in accordance with other linkage groups. Fully informative markers to other genes in this linkage group identified the comparative linkage group in the female map, where recombination ratios determining marker order were similar to the autosomes.
Conclusion
We have created genetic linkage maps that define the 29 linkage groups of the haploid genome, and have revealed the position and extent of the sex-determining locus in A. chinensis. As all Actinidia species are dioecious, we suggest that the sex-determining loci of other Actinidia species will be similar to that region defined in our maps. As the extent of the non-recombining region is limited, our result supports the suggestion that the subtelomeric region of an autosome is in the early stages of developing the characteristics of a sex chromosome. The maps provide a reference of genetic information in Actinidia for use in genetic analysis and breeding programs.
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