title: Different genome-specific chromosome stabilities in synthetic Brassica allohexaploids revealed by wide crosses with Orychophragmus.
abstract: OBJECTIVE
  In sexual hybrids between cultivated Brassica species and another crucifer, Orychophragmus violaceus (2n = 24), parental genome separation during mitosis and meiosis is under genetic control but this phenomenon varies depending upon the Brassica species. To further investigate the mechanisms involved in parental genome separation, complex hybrids between synthetic Brassica allohexaploids (2n = 54, AABBCC) from three sources and O. violaceus were obtained and characterized.
  
  
  METHODS
  Genomic in situ hybridization, amplified fragment length polymorphism (AFLP) and single-strand conformation polymorphism (SSCP) were used to explore chromosomal/genomic components and rRNA gene expression of the complex hybrids and their progenies.
  
  
  RESULTS
  Complex hybrids with variable fertility exhibited phenotypes that were different from the female allohexaploids and expressed some traits from O. violaceus. These hybrids were mixoploids (2n = 34-46) and retained partial complements of allohexaploids, including whole chromosomes of the A and B genomes and some of the C genome but no intact O. violaceus chromosomes; AFLP bands specific for O. violaceus, novel for two parents and absent in hexaploids were detected. The complex hybrids produced progenies with chromosomes/genomic complements biased to B. juncea (2n = 36, AABB) and novel B. juncea lines with two genomes of different origins. The expression of rRNA genes from B. nigra was revealed in all allohexaploids and complex hybrids, showing that the hierarchy of nucleolar dominance (B. nigra, BB > B. rapa, AA > B. oleracea, CC) in Brassica allotetraploids was still valid in these plants.
  
  
  CONCLUSIONS
  The chromosomes of three genomes in these synthetic Brassica allohexaploids showed different genome-specific stabilities (B > A > C) under induction of alien chromosome elimination in crosses with O. violaceus, which was possibly affected by nucleolar dominance.
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, National Center of Crop Molecular Breeding Technology, National Center of Oil Crop Improvement (Wuhan), College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, PR China.
authors.forename: Xian-Hong
authors.initials: XH
authors.lastname: Ge
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Zai-Yun
authors.initials: ZY
authors.lastname: Li
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D001937:Brassica / Q000235:genetics* / Q000502:physiology*; D019607:Brassicaceae / Q000235:genetics* / Q000502:physiology*; D043171:Chromosomal Instability / Q000235:genetics* / Q000502:physiology; D032461:Chromosomes, Plant / Q000235:genetics*; D018745:Genome, Plant / Q000235:genetics*; D006824:Hybridization, Genetic / Q000235:genetics / Q000502:physiology*; D017403:In Situ Hybridization; D018807:Polymorphism, Single-Stranded Conformational / Q000235:genetics; D011123:Polyploidy; D020133:Reverse Transcriptase Polymerase Chain Reaction