Unstable Inheritance of 45S rRNA Genes in Arabidopsis thaliana

• Published in: G3 : genes - genomes - genetics Vol. 7; no. 4; pp. 1201 - 1209
• Main Authors: Rabanal, Fernando A, Nizhynska, Viktoria, Mandáková, Terezie, Novikova, Polina Yu, Lysak, Martin A, Mott, Richard, Nordborg, Magnus
• Format: Journal Article
• Language: English
• Published: England Genetics Society of America 01.04.2017; Oxford University Press
• Subjects: 45S rRNA genes; Arabidopsis - genetics; Arabidopsis thaliana; Crosses, Genetic; DNA Copy Number Variations - genetics; Gene Dosage; Genes, Plant; Genetic Loci; Inbreeding; Inheritance Patterns - genetics; Investigations; natural variation; Nucleolus Organizer Region - genetics; Recombination, Genetic - genetics; Repetitive Sequences, Nucleic Acid - genetics; ribosomes; RNA, Ribosomal - genetics; Arabidopsis thaliana; ribosomes; 45S rRNA genes; natural variation
• ISSN: 2160-1836; 2160-1836
• DOI: 10.1534/g3.117.040204

The considerable genome size variation in has been shown largely to be due to copy number variation (CNV) in 45S ribosomal RNA (rRNA) genes. Surprisingly, attempts to map this variation by means of genome-wide association studies (GWAS) failed to identify either of the two likely sources, namely the nucleolus organizer regions (NORs). Instead, GWAS implicated a -acting locus, as if rRNA gene CNV was a phenotype rather than a genotype. To explain these results, we investigated the inheritance and stability of rRNA gene copy number using the variety of genetic resources available in - F2 crosses, recombinant inbred lines, the multiparent advanced-generation inter-cross population, and mutation accumulation lines. Our results clearly show that rRNA gene CNV can be mapped to the NORs themselves, with both loci contributing equally to the variation. However, NOR size is unstably inherited, and dramatic copy number changes are visible already within tens of generations, which explains why it is not possible to map the NORs using GWAS. We did not find any evidence of -acting loci in crosses, which is also expected since changes due to such loci would take very many generations to manifest themselves. rRNA gene copy number is thus an interesting example of "missing heritability"-a trait that is heritable in pedigrees, but not in the general population.