The Involvement of Taiman in Metamorphasis and Female Reproduction of Helicoverpa Armigera

Abstract

In insects, metamorphosis and reproduction are coordinated by juvenile hormone (JH) and 20-hydroxyecdysone (20E). A transcription factor taiman (Tai) serves as a coactivator of the functional 20E receptor and heterodimerizes with JH receptor Methoprene-tolerant to form an active receptor complex, encoding a key modulator of JH and 20E signaling pathways. However, direct evidence for the involvement of Tai in metamorphic actions and JH-mediated vitellogenesis is quite limited. In this study, only one isoform of Tai was identified from the agricultural pest Helicoverpa armigera, named HaTai. In larvae stage, HaTai was predominately expressed in hemolymph and markedly up-regulated at 5th instar, while in adults HaTai was mainly expressed in females and the highest transcription was detected in ovary and fat body. Knocking down HaTai in 5h-instar larvae caused severe pupation failure and weight loss, wherein 69.44% of HaTai-RNAi larvae died from pupation failure at 6 days post treatment. In female adults, depleting HaTai not only suppressed JH signaling but also blocked vitellogenin transcription and caused atrophied ovaries with deficient yolk protein deposition. The HaTai-depleted females exhibited a substantial decrease in oviposition duration, eggs production, and the hatching rate. Moreover, the HaTai-depleted fat body became remarkably loose and partly vacuolating, accompanied by a reduction of triglyceride content by 8.50%. These results unveiled the complex roles of HaTai in pupation and JH-mediated vitellogenesis in H. armigera, and highlights HaTai as an attractive target to manage lepidopteran pests.

Keywords: Taiman, vitellogenin, pupation, reproduction, fat body, triglyceride