NUCLEAR CYTOPLASMIC INTERACTION HYPOTHESIS AND THE ROLE OF TRANSLOCATIONS IN NICOTIANA ALLOPOLYPLOIDS

摘要

The nuclear cytoplasmic interaction hypothesis (NCI) states that in a newly formed allopolyploid genetic instabilities are induced giving rise to altered paternal genome structure and chromosomal translocations. The hypothesis predicts that plants emerging from a "bottleneck of sterility" are stable, with increased fertility, fixed for particular translocations that are "species-specific", and have a degraded paternal genome. We investigate this hypothesis in the allopolyploids Nicotiana tabacum (tobacco), N. rustica and N. arentsii. Each of these natural allopolyploids have a similar chromosome complement, 2n = 4x = 48. We review the cytological data available for these species. From those studies using genomic in situ hybridisation (GISH) we found evidence in support of NCI only in N. tabacum. To our surprise there is also supporting evidence in the form of structurally similar translocations in a synthetic tobacco line that is only three generations old. These data suggest that the mechanisms of genetic change act early and fast. However in the synthetic material no translocation resolvable by GISH had gone to fixation. Nevertheless the presence of translocations does support the argument that in natural tobacco at least the genomic restructuring that occurred after polyploidy may have facilitated the establishment and stabilisation of the polyploid genome.