A gene-rich linkage map in the dioecious species Actinidia chinensis (kiwifruit) reveals putative X/Y sex-determining chromosomes

Abstract

BackgroundThe 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.ResultsGene-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.ConclusionWe 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.

Mapping, Complementation, and Targets of the Cysteine Protease Actinidin in Kiwifruit

“…This population was used in the recently developed Actinidia linkage map (Fraser et al, 2009), and preliminary data indicated that CP activity segregated within this population (data not shown). As all Actinidia species are functionally dioecious, CP activity measurements could only be made on fruit from the females (n = 133) in the mapping population.…”

“…For these reasons, together with the desire to understand the function of actinidin in planta, we have targeted the nature of CP variation in kiwifruit for study. In this paper, we utilize a gene-rich linkage map in A. chinensis (Fraser et al, 2009) to identify a major quantitative trait locus (QTL) for CP activity and show that it colocates with the gene encoding the major acidic isoform of actinidin. Complementation of ACT1A mutations in transgenic YellowA fruit allowed the physiological consequences of increased CP activity in fruit to be investigated.…”

Applications of Biotechnology in Kiwifruit (Actinidia)

“…The maps were produced with LOD scores ≥2 (as an indication of coinheritance of loci). Continued progress in Actinidia mapping led to a significant advancement in Actinidia genetics, with the generation of a gene-rich linkage map of A. chinensis, constructed using 644 SSRs, and defining the 29 chromosomes of the haploid genome (Fraser et al, 2009). Again, SSRs were the marker of choice, owing to their abundance, distribution in coding and non-coding regions, reproducibility, Mendelian mode of inheritance and co-dominant nature.…”

Floral sesquiterpenes and their synthesis in dioecious kiwifruit

“…9 This system of reproduction is linked to an active Y sex chromosome system (XX/XY female/male) proposed to be in the early stages of evolution. 10 In their natural habitats in south-western China, A. deliciosa flowers are pollinated by a large array of insects, mainly bees, including honey bees, carpenter bees, smaller native bees and bumble bees, but other insects such as hoverflies have also been implicated. 11 In A. polygama it was shown that the major flower visitors were bumble bees, small solitary bees and hoverflies.…”