title: Cytological diploidization and rapid genome changes of the newly synthesized allotetraploids Cucumis x hytivus.
abstract: We used a newly synthesized allotetraploid between C. sativus (2n = 2x = 14, n gametic chromosome number, x haploid chromosome number) and C. hystrix (2n = 2x = 24) to study the genomic events in its early generations. Results from cytological characterization of the F(1) and the allotetraploid progenies showed that the rate of bivalents in meiotic metaphase I of the F(1) was greatly improved by chromosome doubling, and further improved during the selfing process of allopolyploid resulting into relatively diploid-like meiosis. Extensive genomic changes were detected by amplified fragment length polymorphism analysis. The changes mainly involved loss of parental restriction fragments and gaining of novel fragments. The total detectable changes were from 11.1 to 32.1%, and the frequency of losing parental fragments was much higher than that of gaining novel fragments. Some of the changes were initiated as early as in the F(1) hybrid, whereas others occurred after chromosome doubling (polyploid formation). No significant differences were detected in the reciprocal F(1) hybrids and S(0) generations. But the data showed that the frequency of sequence losing in C. sativus was about two times higher than in the C. hystrix. Our results demonstrated that the sequence elimination was the major event of genomic changes, and it might provide the physical basis for the diploid-like meiotic behavior in the diploidization of the newly formed allopolyploids. Moreover, the results suggest that the sequence elimination was not caused by cytoplasmic factors, and might relate to genomic recombination and to the numbers of parental chromosome.
authors.affiliation: State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Horticulture, Nanjing Agricultural University, Nanjing, Jiangsu 210095, People's Republic of China.
authors.forename: Longzheng
authors.initials: L
authors.lastname: Chen
authors.forename: Qunfeng
authors.initials: Q
authors.lastname: Lou
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhuang
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Chen
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Zhang
authors.forename: Joseph N
authors.initials: JN
authors.lastname: Wolukau
mesh_terms: D028462:Cucumis / Q000235:genetics*; D004171:Diploidy; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant / Q000235:genetics*; D008540:Meiosis / Q000235:genetics; D018515:Plant Leaves / Q000235:genetics; D012150:Polymorphism, Restriction Fragment Length; D011123:Polyploidy