RNA-sequencing reveals allelic expression imbalance in the diploid pathogen Candida albicans

The diploid fungal pathogen Candida albicans is a highly heterozygous organism, with numerous non-synonymous substitutions often seen within two alleles. RNA-sequencing of the wild-type strain SC5314 has revealed 233 genes with significant levels of allelic expression imbalance. Overall percentage protein identity comparisons were significantly lower in these differentially expressed alleles. This suggests that two different, perhaps functionally divergent, proteins are being expressed at significantly different quantities by the two alleles of a single gene. Previously, gene expression levels have been correlated with structural factors such as GC content, ORF length and codon usage. Here, these factors were first correlated with overall gene expression data to decipher the relationship they have with gene expression in Candida albicans. These relationships were then used to assess the contribution of these factors to allelic expression imbalance. GC content and codon usage did not differ significantly in differentially expressed alleles whereas ORF length was found to be significantly lower in the allele with lowest expression. This surprising result goes against the overall trend observed between length and gene expression. Differences in GC content and ORF length between alleles correlated strongly with percentage protein identity, suggesting an indirect link between these factors and allelic expression imbalance. One sample (SC5314: wild-type strain) assessed in triplicate and compared to the reference diploid genome