Expression and functional analysis of transformer-2 in Phytoseiulus persimilis and other genes potentially participating in reproductive regulation

Transformer-2 (tra-2) is an important sex-determining gene in insects. It also plays a role in the reproduction of phytoseiid mites. We performed bioinformatic analyses for the tra-2 ortholog in Phytoseiulus persimilis (termed Pptra-2), measured its expression at different stages and quantitatively identified its function in reproduction. This gene encodes 288 amino acids with a conserved RRM domain. The peak of its expression was observed in adult females, especially ca. 5 days after mating. In addition, expression is also higher in eggs than in other stages and adult males. When Pptra-2 was silenced through RNA interference with oral delivery of dsRNA, 56% of the females had their egg hatching rates decreased in the first 5 days, from ca. 100% to ca. 20%, and maintained at low levels during the rest of the oviposition period. To detect other genes functionally related to Pptra-2, transcriptome analyses were performed on day 5 after mating. We compared mRNA expressions among interfered females with significantly reduced egg hatching rate, interfered females without significant hatching rate and CK. In total 403 differential genes were identified, of which 42 functional genes involved in the regulation of female reproduction and embryonic development were screened and discussed.

Mating ecology explains patterns of genome elimination

Genome elimination - whereby an individual discards chromosomes inherited from one parent, and transmits only those inherited from the other parent - is found across thousands of animal species. It is more common in association with inbreeding, under male heterogamety, in males, and in the form of paternal genome elimination. However, the reasons for this broad pattern remain unclear. We develop a mathematical model to determine how degree of inbreeding, sex determination, genomic location, pattern of gene expression and parental origin of the eliminated genome interact to determine the fate of genome-elimination alleles. We find that: inbreeding promotes paternal genome elimination in the heterogametic sex; this may incur population extinction under female heterogamety, owing to eradication of males; and extinction is averted under male heterogamety, owing to countervailing sex-ratio selection. Thus, we explain the observed pattern of genome elimination. Our results highlight the interaction between mating system, sex-ratio selection and intragenomic conflict.