Extensive genome heterogeneity leads to preferential allele expression and copy number-dependent expression in cultivated potato

Abstract

Relative to homozygous diploids, the presence of multiple homologs or homeologs in polyploids affords greater tolerance to mutations that can impact genome evolution. In this study, we describe sequence and structural variation in the genomes of six accessions of cultivated potato (Solanum tuberosum L.), a vegetatively propagated autotetraploid and their impact on the transcriptome. Sequence diversity was high with a mean single nucleotide polymorphisms (SNP) rate of approximately 1 per 50 bases suggestive of high levels of allelic diversity. Additive gene expression was observed in leaves (3605 genes) and tubers (6156 genes) that contrasted the preferential allele expression of between 2180 and 3502 and 3367 and 5270 genes in the leaf and tuber transcriptome, respectively. Preferential allele expression was significantly associated with evolutionarily conserved genes suggesting selection of specific alleles of genes responsible for biological processes common to angiosperms during the breeding selection process. Copy number variation was rampant with between 16 098 and 18 921 genes in each cultivar exhibiting duplication or deletion. Copy number variable genes tended to be evolutionarily recent, lowly expressed, and enriched in genes that show increased expression in response to biotic and abiotic stress treatments suggestive of a role in adaptation. Gene copy number impacts on gene expression were detected with 528 genes having correlations between copy number and gene expression. Collectively, these data suggest that in addition to allelic variation of coding sequence, the heterogenous nature of the tetraploid potato genome contributes to a highly dynamic transcriptome impacted by allele preferential and copy number-dependent expression effects.

Keywords: Solanum tuberosum; copy number variation; gene expression; genetic variation; preferential allele expression.