Prophage-encoded Hm-oscar gene recapitulates Wolbachia-induced male-killing in the tea tortrix moth Homona magnanima

<i>Wolbachia</i> are maternally transmitted bacterial symbionts that are ubiquitous among arthropods. They can hijack host reproduction in various ways, including male-killing (MK), where the sons of infected mothers are killed during development. The recent discovery of MK-associated <i>Wolbachia</i> genes, i.e., <i>oscar</i> in <i>Ostrinia</i> moths and <i>wmk</i> in <i>Drosophila</i> flies, stimulates our interest in the diversity and commonality of MK mechanisms, which remain largely unclear. We recently discovered that a <i>Wolbachia</i> symbiont of the moth <i>Homona magnanima</i> carries an MK-associated prophage region encoding homologs of <i>oscar</i> (<i>Hm-oscar</i>) and <i>wmk</i> (<i>wmk-</i>1-4). Here, we investigated the effects of these genes in the native host. Upon transient overexpression, <i>Hm-oscar</i>, but not <i>wmk</i>, induced male lethality in <i>H. magnanima</i>, in contrast to our observations in <i>Drosophila</i>, where the <i>wmk</i> homologs, but not <i>Hm-oscar</i>, killed the males. <i>Hm-oscar</i> disrupted sex determination in male embryos by inducing a female-type <i>doublesex</i> splicing and impaired dosage compensation, recapitulating the <i>Wolbachia</i> phenotype. Cell-based transfection assays confirmed that <i>Hm-oscar</i> suppressed the function of <i>masculinizer</i>, the primary male sex determinant involved in lepidopteran dosage compensation. Our study highlights the conserved roles of <i>oscar</i> homologs in <i>Wolbachia</i>-induced lepidopteran MK and argues that <i>Wolbachia</i> have evolved multiple MK mechanisms in insects.