Sex-biased gene expression and methylation in the green peach aphid Myzus persicae

Aphids present an ideal system to study insect epigenetics as they can produce diverse, but genetically identical, morphs in response to environmental stimuli. Here, using whole genome bisulphite sequencing and transcriptome sequencing of male and asexual female morphs of the green peach aphid (Myzus persicae), we present the first detailed analysis of cytosine methylation in an aphid and compare the methylation and transcriptional landscapes of male and asexual female morphs. We find that methylation primarily occurs in a CG dinucleotide (CpG) context and that exons are highly enriched for methylated CpGs, particularly at the 3' end of genes. Methylation is positively associated with gene expression, and methylated genes are more stably expressed than un-methylated genes. Male and asexual female morphs have distinct methylation profiles and striking differences were found between the sex chromosome and the autosomes. Autosomal genes are hypo-methylated in males whereas genes belonging to the sex chromosome, which is haploid in males, are hyper-methylated. Overall, we find correlated changes in methylation and gene expression between males and asexual females, and this correlation is particularly strong for genes located on the sex chromosome. Our results suggest that methylation changes may be involved in the regulation of a subset of sex-biased genes, potentially underpinning differentiation between sexual morphs in M. persicae.