The Roles of DNA Methyltransferases 1 (DNMT1) in Regulating Sexual Dimorphism in the Cotton Mealybug, Phenacoccus solenopsis

Abstract

The cotton mealybug, <i>Phenacoccus solenopsis</i>, is an invasive pest that can cause massive damage to many host plants of agricultural importance. <i>P. solenopsis</i> is highly polyphagous, and shows extreme sexual dimorphism between males and females. The functions of DNA methyltransferase (DNMT) enzymes in the cotton mealybug have not been well studied. Here, we carried out an investigation of DNMTs in cotton mealybug to study their roles in sexual dimorphism. We found that the cotton mealybug has two copies of <i>PsDnmt1</i>, but <i>Dnmt3</i> is absent. We then amplified the full-length cDNAs of <i>PsDnmt1A</i> (2,225 bp) and <i>PsDnmt1B</i> (2,862 bp) using rapid amplification cDNA ends (RACE). Quantitative reverse transcriptase PCR shows that both <i>PsDnmt1A</i> and <i>PsDnmt1B</i> are highly expressed in adult males, while the expression of <i>PsDnmt1B</i> is 30-fold higher in gravid females than in virgin females<i>.</i> We knocked down <i>PsDnmt1A</i> and <i>PsDnmt1B</i> with small interfering RNAs (siRNAs), and both genes were successfully down-regulated after 24 h or 72 h in adult females and pupa (<i>t</i>-test, <i>p</i> < 0.05). Down-regulating the expression of these two <i>DNMT</i> genes led to offspring lethality and abnormal body color in adult females. Furthermore, the silencing of <i>PsDnmt1B</i> induced abnormal wing development in emerged adult males. Our results provide evidence that <i>PsDnmt1</i> plays a crucial role in regulating sexual dimorphism in the cotton mealybug.