Unstable Inheritance of 45S rRNA Genes in Arabidopsis thaliana

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Authors

RABANAL Fernando A. NIZHYNSKA Viktoria MANDÁKOVÁ Terezie NOVIKOVA Polina Yu LYSÁK Martin MOTT Richard NORDBORG Magnus

Year of publication 2017
Type Article in Periodical
Magazine / Source G3-Genes, Genomes, Genetics
MU Faculty or unit

Central European Institute of Technology

Citation
Web http://www.g3journal.org/content/7/4/1201
Doi http://dx.doi.org/10.1534/g3.117.040204
Field Genetics and molecular biology
Keywords ribosomes; 45S rRNA genes; natural variation; Arabidopsis thaliana
Description The considerable genome size variation in Arabidopsis thaliana 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 trans-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 A. thaliana 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 trans-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 heritabilitya trait that is heritable in pedigrees, but not in the general population.
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