DNA methylation machinery is involved in development and reproduction in the viviparous pea aphid (Acyrthosiphon pisum)

Abstract

AbstractThe pea aphid (Acyrthosiphon pisum) like the majority of extant aphids displays cyclical parthenogenesis - the ability of mothers to switch the reproductive mode of their offspring from reproducing parthenogenetically to sexually in response to environmental cues. The pea aphid genome encodes two paralogs of thede novoDNA methyltransferase gene,dnmt3aanddnmt3x. Here we show, using phylogenetic analysis, that this gene duplication event occurred at least 106 million years ago, likely after the divergence of the lineage leading to the Aphidomorpha (aphids, phylloxera and adelgids) from that leading to the scale insects (Coccoidea) and that the two paralogs are maintained in the genomes of all aphids examined. We also show that the mRNA of bothdnmt3paralogs are maternally expressed in the viviparous aphid ovary. During development both paralogs are expressed in the germ cells of embryos beginning at stage 5 and persisting throughout development. Chemical inhibition of the DNA methylation machinery leads to defects of oocytes and early stage embryos, and causes a proportion of later stage embryos to be born dead or die soon after birth. These phenotypes suggest a role for DNA methyltransferases in reproduction, consistent with that seen in other insects. Taking the vast evolutionary history of thednmt3paralogs, and the localization of their mRNAs in the ovary, we suggest there is a role fordnmt3aand/ordnmt3xin early development, and a role for DNA methylation machinery in reproduction and development of the viviparous pea aphid.