In Riptortus pedestris (Hemiptera, Alydidae), adult females develop their ovaries under long-day conditions (LD), but enter reproductive diapause with suppression of ovarian development under short-day conditions (SD). This photoperiodic response is regulated by juvenile hormone (JH). Krüppel homolog 1 (Kr-h1) encodes a JH-inducible transcriptional factor and plays a pivotal role for reproduction in some insects. In the present study, we molecularly characterized Kr-h1 and investigated Kr-h1 expression patterns under SD and LD in R. pedestris. The open reading frame of Kr-h1 was 1320 bp encoding a protein of 440 amino acids. The deduced protein contained eight conserved C2H2-type zinc finger domains. The expression levels of Kr-h1 increased from 5 days and peaked at 7 days after transfer from SD to LD. By contrast, Kr-h1 was constantly expressed at a low level under SD. Topical application of a JH analogue induced ovarian development and Kr-h1 expression even under SD, suggesting that Kr-h1 is a JH-inducible gene in R. pedestris. Then, we examined the effect of knockdown of circadian clock genes Clock (Clk) and mammalian-type cryptochrome (cry-m) by RNA interference (RNAi) on the ovarian development and Kr-h1 expression. Clk RNAi prevented ovarian development and decreased the Kr-h1 expression under LD, whereas cry-m RNAi induced ovarian development and Kr-h1 expression under SD. These results imply that JH secretion is prevented by Clk RNAi under LD and induced by cry-m RNAi under SD. From these results, we suggest that Kr-h1 expression is JH dependent and closely correlates with photoperiodic regulation of ovarian development.
