Frequent variations in tandem repeats pSc200 and pSc119.2 cause rapid chromosome evolution of open-pollinated rye

Abstract

Variation in heterochromatin is thought to play an important role in chromosome evolution in cereal rye (Secale cereale). This theory has been based on only limited numbers of sampled individuals, as it is difficult to handle large numbers in detailed cytogenetic analyses. In this study, we analyzed a relatively large number of individuals comprising 300 plants from six open-pollinated rye cultivars using oligonucleotides TAMRA-oligo-6 and FAM-pSc119.2-1 that represent tandem repeats of pSc200 and pSc119.2, respectively. Seventy-three types of heterochromatin blocks were identified on all seven chromosomes: 43 from pSc119.2 and 30 from pSc200. Eight block types were fully conserved, and variants in 65 (89.04%) had frequencies ranging from 0.17 to 49.67% and an average of 14.47%. Block 6R-g3 (49.67%) had the highest frequency of variation. Higher average frequencies of variation in block types were revealed by pSc200 (19.33%) than by pSc119.2 (11.08%). A total of 322 polymorphic chromosomes (combinations of different block types) were identified, including 79 major types with frequencies higher than expected, including 14 that were fivefold higher. Six preferentially transmitted chromosomes were confirmed by karyotype analysis in 40 wheat-rye F1 plants. Among the 300 plants investigated, there were 63.00 to 86.66% heterozygosity and 43.66 to 90.32% heterogeneity for each chromosome. Results from this research confirmed rapid chromosome change and high levels of chromosome diversity in heterochromatin blocks in rye.