Retrotransposons are mobile genetic elements abundant in plant and animal genomes. While efficiently silenced by the epigenetic machinery, they can be reactivated upon stress or during development. Their level of transcription not reflecting their transposition ability, it is thus difficult to evaluate their contribution to the active mobilome. Here we applied a simple methodology based on the high throughput sequencing of extrachromosomal circular DNA (eccDNA) forms of active retrotransposons to characterize the repertoire of mobile retrotransposons in plants. This method successfully identified known active retrotransposons in both Arabidopsis and rice material where the epigenome is destabilized. When applying mobilome-seq to developmental stages in wild type rice, we identified PopRice as a highly active retrotransposon producing eccDNA forms in the wild type endosperm. The mobilome-seq strategy opens new routes for the characterization of a yet unexplored fraction of plant genomes.

Myogenic factor 5 (Myf5), a product of the Myf5 gene, belongs to the MRF family of basic helix-loop-helix transcription factors that regulate myogenesis. Their roles in muscle growth and development make their genes candidates for molecular markers of meat production in livestock, but nucleotide sequence polymorphism has not been thoroughly studied in MRF genes. We detected four single nucleotide polymorphisms (SNPs) within exon 1 of the Myf5 gene, encoding the NH-terminal transactivation domain of the Myf5 protein. Three of these mutations change the amino acid sequence. The distribution of these SNPs was highly skewed in cattle populations; most of the mutations were found in only a few or even single individuals. Of the nine SNPs found in the promoter region of Myf5, one (transversion g.-723G-->T) was represented by all three genotypes distributed in the cattle populations studied. This polymorphism showed an influence on Myf5 gene expression in the longissimus dorsi muscle and was associated with sirloin weight and fat weight in sirloin in carcasses of Holstein-Friesian cattle.

The objective of the study reported in this Research Communication was to investigate the association of polymorphisms in the insulin-like growth factor receptor 2 (IGF2R) gene with milk traits in 283 Polish Holstein-Friesian (PHF) cows from the IGAB PAS farm in Jastrzębiec. IGF2R regulates the availability of biologically active IGF2 which is considered as a genetic marker for milk or meat production in farm animals. Two novel genetic polymorphisms were identified in the bovine IGF2R gene: a polymorphic TG-repeat in intron 23 (g.72389 (TG)15-67), and a g.72479 G > A SNP RFLP-StyI in exon 24. The following milk traits were investigated: milk yield, protein and fat yield, SCC and lactose content. To determine the influence of the IGF2R STR and SNP genotypes on the milk traits, we used the AI-REML (average information restricted maximum likelihood) method with repeatability, multi-trait animal model based on test-day information using DMU package. Statistical analysis revealed that the G/A genotype (P ≤ 0·01) was associated with milk and protein yield, lactose content and somatic cell count (SCC) in Polish HF cows. TGn (29/22, 28/29, 28/22, 28/28) genotypes were associated with high values for milk, (28/22, 28/23) with protein and fat yield, (25/20) with lactose content, and (29/33, 28/28) with low SCC. We suggest that the IGF2R gene polymorphisms could be useful genetic markers for dairy production traits in cattle.