Genome and transcriptome analysis of the mealybug Maconellicoccus hirsutus: A model for genomic Imprinting

In mealybugs, transcriptional inactivation of the entire paternal genome in males, due to genomic imprinting, is closely correlated with sex determination. The sequencing, de-novo assembly and annotation of the mealybug, Maconellicoccus hirsutus genome and its comparison with Planococcus citri genome strengthened our gene identification. The expanded gene classes, in both genomes relate to the high pesticide and radiation resistance; the phenotypes correlating with increased gene copy number rather than the acquisition of novel genes. The complete repertoire of genes for epigenetic regulation and multiple copies of genes for the core members of polycomb and trithorax complexes and the canonical chromatin remodelling complexes are present in both the genomes. Phylogenetic analysis with Drosophila shows high conservation of most genes, while a few have diverged outside the functional domain. The proteins involved in mammalian X-chromosome inactivation are identified in mealybugs, thus demonstrating the evolutionary conservation of factors for facultative heterochromatization. The transcriptome analysis of adult male and female M.hirsutus indicates the expression of the epigenetic regulators and the differential expression of metabolic pathway genes and the genes for sexual dimorphism. The depletion of endosymbionts in males during development is reflected in the significantly lower expression of endosymbiont genes in them.