Abstract
Interploidy cross commonly results in complex chromosome number and structural variations. In our previous study, a progeny with segregated ploidy levels was produced by an interploidy cross between diploid female parent Populus tomentosa × Populus bolleana clone TB03 and triploid male parent Populus alba × Populus berolinensis ‘Yinzhong’. However, the chromosome compositions of aneuploid genotypes in the progeny were still unclear. In the present study, a microsatellite DNA allele counting–peak ratios (MAC-PR) method was employed to analyze allelic configurations of each genotype to clarify their chromosome compositions, while 45S rDNA fluorescence in situ hybridization (FISH) analysis was used to reveal the mechanism of chromosome number variation. Based on the MAC-PR analysis of 47 polymorphic simple sequence repeat (SSR) markers distributed across all 19 chromosomes of Populus, both chromosomal number and structural variations were detected for the progeny. In the progeny, 26 hypo-triploids, 1 hyper-triploid, 16 hypo-tetraploids, 10 tetraploids, and 5 hyper-tetraploids were found. A total of 13 putative structural variation events (duplications and/or deletions) were detected in 12 genotypes, involved in chromosomes 3, 6, 7, 14, 15, 16, and 18. The 46.2% (six events) structural variation events occurred on chromosome 6, suggesting that there probably is a chromosome breakpoint near the SSR loci of chromosome 6. Based on calculation of the allelic information, the transmission of paternal heterozygosity in the hypo-triploids, hyper-triploid, hypo-tetraploids, tetraploids, and hyper-tetraploids were 0.748, 0.887, 0.830, 0.833, and 0.836, respectively, indicating that the viable pollen gains of the male parent ‘Yinzhong’ were able to transmit high heterozygosity to progeny. Furthermore, 45S rDNA–FISH analysis showed that specific-chromosome segregation feature during meiosis and chromosome appointment in normal and fused daughter nuclei of telophase II of ‘Yinzhong,’ which explained that the formation of aneuploids and tetraploids in the progeny could be attributed to imbalanced meiotic chromosomal segregation and division restitution of ‘Yinzhong,’ The data of chromosomal composition and structural variation of each aneuploid in the full-sib progeny of TB03 × ‘Yinzhong’ lays a foundation for analyzing mechanisms of trait variation relying on chromosome or gene dosages in Populus.
Highlights
Chromosome number variation, such as euploidy and aneuploidy variation, commonly leads to extensive phenotypic changes, which have been widely used in breeding programs of plants
According to the allele data of the 12 markers in progeny, we found that the female parent TB03 only contributed one locus in all progeny (Supplementary Table 2), suggesting that the female parent TB03 only contributed normal eggs in the interploidy hybridization
The microsatellite DNA allele counting–peak ratios (MAC-PR) method was successfully used in quantification of the allele copy number of Populus aneuploids
Summary
Chromosome number variation, such as euploidy and aneuploidy variation, commonly leads to extensive phenotypic changes, which have been widely used in breeding programs of plants. According to the loss or gain of chromosome(s) from euploid, aneuploid commonly can be classified into two basic types: hypo- and hyper-euploid. Both types of aneuploids could be produced by crossing with polyploids because imbalanced meiotic chromosome segregation and chromosome elimination of polyploids can result in the formation of aneuploid gametes. In Arabidopsis thaliana, Henry et al (2005) produced a swarm of different aneuploids by self-pollination of triploids, and revealed that chromosome composition and dosage variation strongly result in phenotypic changes (Henry et al, 2010). Chromosome manipulation based on aneuploids has attracted increasing attention for improving the efficiency in plant breeding
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