Expression analysis of pea aphid cuticular protein genes in response to “resistant” and “susceptible” alfalfa cultivars.

Pea aphid (Acyrthosiphon pisum) is an important pest of alfalfa fields that gravely impacts the yield and quality of alfalfa (Medicago sativa). To get insights into the molecular mechanisms of the adaption of pea aphids to alfalfa, this study examined the expression levels of six cuticular protein genes (ApCP7, ApCP10, ApCP19, ApCP35, ApCP62, and ApCP19.8-like) that consumed two varieties of alfalfa, “Hunter River” (susceptible) and ”Gannong No. 5” (resistant). The survival rate of pea aphids with silenced cuticular protein genes (ApCP7 and ApCP62) was also determined in the ‘Hunter River’ alfalfa. The results indicated that compared to feeding on ‘Hunter River’ alfalfa, the expression levels of the six cuticular protein genes in pea aphids were significantly downregulated in the head (P < 0.01) and upregulated in the ovaries (P < 0.01) after feeding on ‘Gannong No. 5’ alfalfa. In abdominal tissues, apart from the significant upregulation of the cuticular protein gene ApCP7 (P < 0.01), the expression levels of the other genes were significantly downregulated (P < 0.01); ApCP7, ApCP19, ApCP19.8-like, and ApCP62 were significantly upregulated in cuticular tissues (P < 0.05). Following the silencing of cuticular protein genes ApCP7 and ApCP62, the survival rates of pea aphids feeding on ‘Hunter River’ alfalfa were significantly reduced (P < 0.05) to 76.67% and 80.67% after 72 h, respectively. According to these results, we infer that ApCP7 and ApCP62 are involved in pea aphid adaptation to alfalfa varieties with different resistance levels and provide a theoretical foundation for elucidating the interaction between pea aphids and alfalfa.