Differential expression, phosphorylation of COX subunit 1 and COX activity during diapause phase in the cotton bollworm, Helicoverpa armigera

Abstract

Helicoverpa armigera (Lepidoptera, Noctuidae) is an important agricultural pest with a pupal diapause. Cytochrome c oxidase (COX) is a key speed-limited enzyme of oxidative phosphorylation in mitochondria for ATP production. A differentially expressed cDNA fragment encoding COX subunit 1 (cox1) was cloned by differential display-PCR from the pupal brain at diapause termination with an injection of ecdysone. We then obtained the full length of H. armigera cox1 (Hea-cox1) cDNA which has an open reading frame of 1530 nucleotides encoding a putative protein of 510 amino acid residues, with CGA as a start codon. To evaluate the response to different energy demands during pupal development and at diapause termination, we assessed the expression of Hea-cox1 mRNA and protein, COX activity and its phosphorylation. The results show that Hea-cox1 expression at the mRNA and protein levels is associated with COX activity, and high levels of Hea-cox1 expression and COX activity are present in nondiapause pupae, suggesting that low energy metabolism provided by oxidative phosphorylation in mitochondria in diapause individuals is necessary. After diapause is broken by injection of 20-hydroxyecdysone, expression of Hea-cox1 mRNA and protein increases gradually and COX activity increases significantly. Furthermore, Hea-cox1 phosphorylation is closely correlated with COX activity, suggesting that reversible protein phosphorylation may play a key role in insect diapause by suppressing the rate of energy production.