Abstract
Nuclear-cytoplasmic interactions are predicted to be important in shaping the genetic changes in early stage of allopolyploidization. Our previous study shows the specific role of genome and cytoplasm affecting the chromosome pairing in Brassica hybrids and allotetraploids from pairwise crosses between three cultivated diploids with A, B and C genomes, respectively. Herein, to address how parental genomes and cytoplasm affects genomic, epigenetic and gene expression changes prior to meiosis in these hybrids and allopolyploids, their patterns of AFLP (Amplified fragment length polymorphism), mAFLP (Methylation AFLP) and cDNA-AFLP were compared with the progenitors, revealing the major absent bands within each genome. These changes varied under various cytoplasm backgrounds and genome combinations, following the significant order of AFLP> mAFLP> cDNA -AFLP. The frequencies of AFLP bands lost were positively correlated with the divergence degrees of parental genomes, but not obvious for those of mAFLP and cDNA-AFLP absent bands, and methylation change showed least variations among hybrids and within each genome. These changes within each genome followed the A>B>C hierarchy, except the highest rate of cDNA loss in B genome. Among three changes, only overall AFLP bands were significantly correlated with cDNA-AFLP, and their correlations varied within each genome. These changes in allotetraploids were mainly caused by genome merger rather than doubling. Parental genomes altered differently at three levels, responded to the types of cytoplasm and genome and their interaction or divergence. The result provides new clues for instant non-meiosis-driven genome restructuring following genome merger and duplication.
Highlights
Interspecific hybridizations and formation of alloployploids with genomes from two or more related parental species have contributed to the origins of many higher plants
Genetic changes in the S5 progenies of,50 resynthesized B. napus lines (CC.AA) occurred more frequently in the C-genome, while cytosine methylation changes occurred more frequently in the A-genome [6]; DNA fragment losses in this synthetics were significantly correlated with cDNA-AFLP fragment losses, but methylation changes were not correlated, suggesting that genomic rearrangements were largely responsible for loss of cDNA-AFLP markers
DNA, RNA Extraction, and cDNA Synthesis To ensure the homogenous identity of each hybrid or allotetraploid, at least five plantlets from one embryo of each cross were produced by successive subculturing on the MS [34] medium with 1.5 mg/L 6-benzyl aminopurine (6-BA), 0.25 mg/L a-naphthalenacetic acid (NAA) and transferred in the field
Summary
Interspecific hybridizations and formation of alloployploids with genomes from two or more related parental species have contributed to the origins of many higher plants. The dynamic nature of polyploid genomes is recognized [20], though the degrees of variations are markedly different between allopolyploids [21,22]. In reciprocal synthetics of B. napus and B. juncea, using the diploid species as maternal and paternal genome donors (AA.CC - CC.AA and AA.BB - BB.AA), the frequency of genetic change was influenced by the parental origin of the genomes, and the same genome showed more change when provided by the male parent [26]. Higher frequencies of genome change in B. juncea than in B. napus are considered to be associated with higher degrees of divergence between the parental A and B genomes than between A and C genome, or the nuclear-cytoplasmic incompatibility, because of the more closely related A and C cytoplasmic genomes and to the more compatible nuclear-cytoplasmic genomes in the AC and CA polyploids.
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