Intra- and intergenomic homology of B-genome chromosomes in trigenomic combinations of the cultivated Brassica species revealed by GISH analysis.
Intragenomic chromosome homology in the B genome of Brassica nigra and their homoeology with the chromosomes of the A-genome of B. rapa and C-genome of B. oleracea was investigated in triploids (ABC, n = 27) of different origins obtained following hybridizations between natural B. napus (AACC, 2n = 38) x B. nigra (BB, 2n = 16) [AC.B], synthetic B. napus x B. nigra [A.C.B] and B. carinata (BBCC, 2n = 34) x B. rapa (AA, 2n = 20) [BC.A]. A relatively high percentage of pollen mother cells (PMCs) with at least one B-genome chromosome paired allosyndetically with A/C chromosomes was evident in all three combinations. A maximum of three B-genome chromosomes undergoing allosyndesis per cell was observed in AC.B and A.C.B combinations. A maximum of two autosyndetic bivalents within the B genome appeared at diakinesis in all combinations. The accurate analyses of auto- and allo-syndetic pairing for B genome in trigenomic combinations provided further evidence for the hypothesis that the three basic diploid genomes of the cultivated Brassica species evolved from one common ancestral genome with a lower chromosome number. The results showed that Brassica diploids may not be ancient polyploids but may have undergone chromosomal duplications instead of whole-genome duplication. The relevance of these results along with genetic changes of progenitor genomes which occurred during the evolution of Brassica polyploids is discussed.
Ge
Xian-Hong
XH
National Key Laboratory of Crop Genetic Improvement, National Center of Crop Molecular Breeding Technology, National Center of Oil Crop Improvement (Wuhan), Huazhong Agricultural University, Wuhan, 430070, PR China.
Li
Zai-Yun
ZY
D005075:Biological Evolution; D001937:Brassica / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D023902:Chromosome Pairing; D032461:Chromosomes, Plant / Q000235:genetics*; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000032:analysis / Q000302:isolation & purification; D018745:Genome, Plant; D017403:In Situ Hybridization / Q000379:methods*
D018744:DNA, Plant