Regulation of <i>Krüppel homolog 1</i> expression by photoperiod in the bean bug, <i>Riptortus pedestris</i>

<jats:title>Abstract</jats:title><jats:p>In <jats:italic>Riptortus pedestris</jats:italic> (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). <jats:italic>Krüppel homolog 1</jats:italic> (<jats:italic>Kr‐h1</jats:italic>) encodes a JH‐inducible transcriptional factor and plays a pivotal role for reproduction in some insects. In the present study, we molecularly characterized <jats:italic>Kr‐h1</jats:italic> and investigated <jats:italic>Kr‐h1</jats:italic> expression patterns under SD and LD in <jats:italic>R</jats:italic>. <jats:italic>pedestris</jats:italic>. The open reading frame of <jats:italic>Kr‐h1</jats:italic> was 1320 bp encoding a protein of 440 amino acids. The deduced protein contained eight conserved C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>‐type zinc finger domains. The expression levels of <jats:italic>Kr‐h1</jats:italic> increased from 5 days and peaked at 7 days after transfer from SD to LD. By contrast, <jats:italic>Kr‐h1</jats:italic> was constantly expressed at a low level under SD. Topical application of a JH analogue induced ovarian development and <jats:italic>Kr‐h1</jats:italic> expression even under SD, suggesting that <jats:italic>Kr‐h1</jats:italic> is a JH‐inducible gene in <jats:italic>R</jats:italic>. <jats:italic>pedestris</jats:italic>. Then, we examined the effect of knockdown of circadian clock genes <jats:italic>Clock</jats:italic> (<jats:italic>Clk</jats:italic>) and <jats:italic>mammalian‐type cryptochrome</jats:italic> (<jats:italic>cry‐m</jats:italic>) by RNA interference (RNAi) on the ovarian development and <jats:italic>Kr‐h1</jats:italic> expression. <jats:italic>Clk</jats:italic> RNAi prevented ovarian development and decreased the <jats:italic>Kr‐h1</jats:italic> expression under LD, whereas <jats:italic>cry‐m</jats:italic> RNAi induced ovarian development and <jats:italic>Kr‐h1</jats:italic> expression under SD. These results imply that JH secretion is prevented by <jats:italic>Clk</jats:italic> RNAi under LD and induced by <jats:italic>cry</jats:italic>‐<jats:italic>m</jats:italic> RNAi under SD. From these results, we suggest that <jats:italic>Kr‐h1</jats:italic> expression is JH dependent and closely correlates with photoperiodic regulation of ovarian development.</jats:p>