Krüppel homolog 1 mediates juvenile hormone action to suppress photoperiodic reproductive diapause-related phenotypes in the female Chrysoperla nipponensis (Neuroptera: Chrysopidae)

Abstract

Juvenile hormone (JH) has been revealed to be a critical factor in regulating photoperiod reproductive diapause in various insect species, however, little information is known about the detailed mechanisms. In this study, we investigated the roles of JH signaling in photoperiod reproductive diapause in a green lacewing, Chrysoperla nipponensis (Okamoto), which is a potentially important biological control predator. Our results showed that the short-day condition induces a diapause state including JH synthesis suppression, ovarian development arrest, and triglyceride accumulation. The interference of JH response genes, Krüppel homolog 1 (Kr-h1), in reproductive females exhibited a diapause-related phenotype such as ovarian development arrest and larger triglyceride storage. Exogenous JH III suppresses diapause to promote ovarian development and inhibit triglyceride synthesis. However, exogenous JH III fails to rescue the Kr-h1-silenced phenotype. Accordingly, our results demonstrate the critical role of Kr-h1 in regulating JH signaling to promote reproduction.

Keywords: Krüppel-homolog 1; green lacewing; juvenile hormone; photoperiod; reproductive diapause.

Fig. 1.

Effects of photoperiod on JH synthesis and JH-related gene expression in C. nipponensis. (A) The JH III (ng/g female lacewings) in C. nipponensis reared under LD and SD photoperiod. Expression profiles of Jhamt (B), Kr-h1 (C), and Vg (D) in intact C. nipponensis reared under LD and SD photoperiod. Data are shown as mean ± SE. Student’s t-test was used to analyze the statistical significance of the difference between the means of the two treatment groups (*P < 0.05, **P < 0.01). *indicates that the gene expression of C. nipponensis is significantly different on the same day under the long and short photoperiods (*P < 0.05; **P < 0.01), LD: long-day (15:9 h light:dark); SD: short-day (9:15 h light: dark).

Fig. 2.

Effects of SD photoperiod on females’ ovarian development and lipid accumulation in C. nipponensis. The morphology of ovarian development (A) and the ovariole length (B) in C. nipponensis females at 1, 3, 5, and 10 d post-eclosion under LD and SD photoperiod. The triglyceride content in C. nipponensis females at 10 d post-eclosion under long and short photoperiods (C). Expression patterns of Kr-h1 (D) and Vg (E) in the fat body of C. nipponensis females. Data are shown as mean ± SE. Student’s t-test was used to analyze the statistical significance of difference between the means of the 2 treatment groups. *indicates that the gene expression of C. nipponensis is significantly different in treatment groups (*P < 0.05; **P < 0.01), LD: long-day (15:9 h light:dark); SD: short-day (9:15 h light:dark).

Fig. 3.

Effects of JHIII on female of C. nipponensis. Under the SD photoperiod, the morphology of the ovary (A), the ovariole length (B), and the triglyceride content (C) after exogenous JHIII treatment. Expression of Kr-h1 (D) and Vg (E) in the fat body after exogenous JHIII treatment. Data are shown as mean ± SE. Student’s t-test was used to analyze the statistical significance of the difference between the means of the 2 treatment groups (*P < 0.05, **P < 0.01). LD: long-day (15:9 h light:dark); SD: short-day (9:15 h light:dark).

Fig. 4.

Effects of Kr-h1 on diapause-related phenotype of C. nipponensis. Under the LD photoperiod, the effects of Kr-h1-interfering on the expression of Kr-h1 (A) and Vg (B), the morphology of the ovary (C), the ovarian length (D), and the triglyceride content (E). Student’s t-test was used to analyze the statistical significance of the difference between the means of the 2 treatment groups (*P < 0.05, **P < 0.01). LD: long-day (15:9 h light:dark); SD: short-day (9:15 h light:dark).

Fig. 5.

Effect of JH and Kr-h1 on female of C. nipponensis. Under the LD photoperiod, after ds-Kr-h1 injection, the effects of JHIII on the expression of Kr-h1 (A) and Vg (B). The rescue of JHIII on the morphology of the ovary (C), the ovarian length (D), and the triglyceride content (E). Data are shown as mean ± SE. Student’s t-test was used to analyze the statistical significance of the difference between the means of the two treatment groups (*P < 0.05, **P < 0.01). LD: long-day (15:9 h light:dark); SD: short-day (9:15 h light:dark).

Fig. 6.

Schematic view of JH signaling and Kr-h1 regulates reproduction and diapause in C. nipponensis. Under LD conditions, corpora allata (CA) synthesizes JH in C. nipponensis females, and then JH stimulates Kr-h1 expression. Thus, Kr-h1 promotes the ovary development but suppresses lipid accumulation in the fat body. Contrarily, under the SD, JH production is blocked, and Kr-h1-mediated JH signaling is then absent, thereby triggering diapause traits.