Genome or genomic dominance (GD) is a phenomenon observed in hybrids when one parental genome becomes dominant over the other. It is manifested by the replacement of chromatin of the submissive genome by that of the dominant genome and by biased gene expression. Nucleolar dominance (ND) - the functional expression of only one parental set of ribosomal genes in hybrids - is another example of an intragenomic competitive process which, however, concerns ribosomal DNA only. Although GD and ND are relatively well understood, the nature and extent of their potential interdependence is mostly unknown. Here, we ask whether hybrids showing GD also exhibit ND and, if so, whether the dominant genome is the same. To test this, we used hybrids between Festuca and Lolium grasses (Festulolium), and between two Festuca species in which GD has been observed (with Lolium as the dominant genome in Festulolium and F. pratensis in interspecific Festuca hybrids). Using amplicon sequencing of ITS1 and ITS2 of the 45S ribosomal DNA (rDNA) cluster and molecular cytogenetics, we studied the organization and expression of rDNA in leaf tissue in five hybrid combinations, four generations and 31 genotypes [F. pratensis × L. multiflorum (F1, F2, F3, BC1), L. multiflorum × F. pratensis (F1), L. multiflorum × F. glaucescens (F2), L. perenne × F. pratensis (F1), F. glaucescens × F. pratensis (F1)]. We have found that instant ND occurs in Festulolium, where expression of Lolium-type rDNA reached nearly 100% in all F1 hybrids and was maintained through subsequent generations. Therefore, ND and GD in Festulolium are manifested by the same dominant genome (Lolium). We also confirmed the concordance between GD and ND in an interspecific cross between two Festuca species.

• Klíčová slova
• Festuca, Lolium, fluorescent in situ hybridization, genome dominance, genomic in situ hybridization, internal transcribed spacer, nucleolar dominance, ribosomal DNA,
• Publikační typ
• časopisecké články MeSH

Genome dominance is a phenomenon in wide hybrids when one of the parental genomes becomes "dominant," while the other genome turns to be "submissive." This dominance may express itself in several ways including homoeologous gene expression bias and modified epigenetic regulation. Moreover, some wide hybrids display unequal retention of parental chromosomes in successive generations. This may hamper employment of wide hybridization in practical breeding due to the potential elimination of introgressed segments from progeny. In onion breeding, Allium roylei (A. roylei) Stearn has been frequently used as a source of resistance to downy mildew for cultivars of bulb onion, Allium cepa (A. cepa) L. This study demonstrates that in A. cepa × A. roylei hybrids, chromosomes of A. cepa are frequently substituted by those of A. roylei and in just one generation, the genomic constitution shifts from 8 A. cepa + 8 A. roylei chromosomes in the F1 generation to the average of 6.7 A. cepa + 9.3 A. roylei chromosomes in the F2 generation. Screening of the backcross generation A. cepa × (A. cepa × A. roylei) revealed that this shift does not appear during male meiosis, which is perfectly regular and results with balanced segregation of parental chromosomes, which are equally transmitted to the next generation. This indicates that female meiotic drive is the key factor underlying A. roylei genome dominance. Single nucleotide polymorphism (SNP) genotyping further suggested that the drive has different strength across the genome, with some chromosome segments displaying Mendelian segregation, while others exhibiting statistically significant deviation from it.

• Klíčová slova
• female meiosis, genome stability, homoeologous recombination, homoploid, interspecific hybridization, meiotic drive, onion,
• Publikační typ
• časopisecké články MeSH