A molecular cytogenetic analysis of chromosome behavior in Lilium ...

General IntroductionSome basic concepts on geneticsWhen an interspecific cross is made, the alien genome is introduced into a new geneticbackground, and the hybrids may undergo genomic shock (Chen and Ni 2006; McClintock1984; Natali et al. 1998). The instability in new-synthesized interspecific hybrids caused bygenomic shock underlies rapid genome changes in the following generations, such genomechanges caused by complex intergenomic interaction consists of polyploidization,chromosome rearrangements (structural chromosome aberrations), gene conversion,aneuploidy and so on (Soltis and Soltis 2000), which are considered to be important in plantpolyploids. As a result, extensive intergenomic exchanges were conclusively proven to haveoccurred in many allopolyploids, both revealed by DNA in situ hybridization and molecularmarkers (Brubaker et al. 1999; Osborn et al. 2003; Pontes et al. 2004).Recently, the so called chromosome rearrangements in allopolyploids were extensivelyanalyzed in a few natural and re-synthesized allopolyploids. Among others, Brassica napussupplies a good example in point. B. napus is believed to originated from interspecifichybridization between B. oleracea (CC, 2n=18) and B. rapa (AA, 2n=20) followed bypolyploidization (U 1935). When analyzing these natural and synthetic tetraploid B. napuspopulations with molecular markers, various types of “chromosome rearrangements” weredetected, such as homoeologous non-reciprocal translocation, homoeologous reciprocaltranslocation, duplication, deletion and so on (Osborn et al. 2003; Parkin et al. 1995; Sharpeet al. 1995). Later on, it was confirmed that homoeologous recombination during meiosis ofthe haploid B. napus is the main reason of the genetic changes (Gaeta and Pires 2010; Gaetaet al. 2007; Nicolas et al. 2007; Xiong et al. 2011). In addition, genome changes, viz. deletion,duplication, inversion and so on, were also proven to be present by comparing the naturalallopolyploids with the re-synthesized allopolyploids or their progenitors, in Arabidopsissuecica which is derived from cross between two diploid Arabidopsis species (Arabidopsisthaliana and A. arenosa)(O'Kane Jr et al. 1996; Pontes et al. 2004), in amphidiploid Nicotianatabacum (Kenton et al. 1993), in cultivated Gossipium (Brubaker et al. 1999; Reinisch et al.1994), in Avena maroccana (Leitch and Bennett 1997; Soltis and Soltis 1999), in Avenasativa (Chen and Armstrong 1994), in allotetraploid Tragopogon (Lim et al. 2008b) and manyother species.Genetic changes induced by genomic shock in early generations not only contribute tospeciation of hybrids, but also supply diverse materials for plant breeding. Those abovementioned non-Mendelian and rapid genome reconstruction might be a mechanism forgenerating de novo genomic variation and increasing genetic and morphological complexity,which may partly explain the evolutionary success of allopolyploids over their diploid3