20-Hydroxyecdysone in Silkworm Biology: Molecular Mechanisms of Biosynthesis, Development and Biotechnological Applications
Nikita Kankanawadi
*
Department of Sericulture College of Agriculture, University of Agricultural Sciences, Gandhi Krishi Vigyana Kendra, Bengaluru – 560065, India.
Veenita M. K.
Department of Sericulture College of Agriculture, University of Agricultural Sciences, Gandhi Krishi Vigyana Kendra, Bengaluru – 560065, India.
Shwetha G. V.
Department of Sericulture College of Agriculture, University of Agricultural Sciences, Gandhi Krishi Vigyana Kendra, Bengaluru – 560065, India.
Kaveri Aramani
Department of Sericulture College of Agriculture, University of Agricultural Sciences, Gandhi Krishi Vigyana Kendra, Bengaluru – 560065, India.
Gagana Sindhu S.
Department of Sericulture College of Agriculture, University of Agricultural Sciences, Gandhi Krishi Vigyana Kendra, Bengaluru – 560065, India.
Tejaswini A. S.
Department of Sericulture College of Agriculture, University of Agricultural Sciences, Gandhi Krishi Vigyana Kendra, Bengaluru – 560065, India.
*Author to whom correspondence should be addressed.
Abstract
20-Hydroxyecdysone (20E), a crucial steroid hormone in insects, plays a multifaceted role in regulating the developmental, physiological, and metabolic processes of the silkworm Bombyx mori. This review comprehensively covers its function across distinct developmental stages—embryonic, larval, and pupal. During embryogenesis and larval development, 20E biosynthesis depends on the maternal 3-epimerization pathway and key enzymes such as ecdysone oxidase (BmEO) and 3DE-3β-reductase. Functional studies show that disruption of these genes results in reduced ecdysone levels, developmental arrest, and decreased hatching rates. Notably, noppera-bo (nobo-Bm), a glutathione S-transferase gene involved in ecdysteroidogenesis, shows over 10-fold higher expression in the ovary, and its loss-of-function mutations cause larval lethality due to impaired sterol utilization. Beyond development, 20E plays a vital role in immune modulation by inducing antimicrobial peptides via the Broad-Complex Z2 (Br-C Z2) transcription factor and facilitates genital disc differentiation through the MAPK signalling pathway. In applied sericulture, the expression of the baculovirus-derived EGT gene in transgenic silkworms suppresses 20E levels, leading to prolonged larval feeding, inhibition of pupation, and a significant increase in cocoon shell ratio, thereby enhancing silk yield. Collectively, these insights highlight the central regulatory role of 20E across silkworm development and physiology, and underscore its biotechnological potential for improving sericultural productivity.
Keywords: Diapause, silkworm, biosynthesis, maternal, 20-Hydroxyecdysone, ecdysteroids