Molecular Mechanisms of Climate Stress Tolerance in Silkworms: Insights for Sustainable Sericulture among Farmers

Abstract

Climate change represents a serious and growing threat to the sericulture industry in India and across the world. Silkworms being obligate ectotherms are severely sensitive to environmental changes, especially during their critical developmental stages i.e., 4th and 5th instars. This affects their biology including glucose and lipid metabolism, oxidative phosphorylation, cocoon development and ultimately results in reduced silk production and inferior silk quality. In this review the complex molecular defence mechanisms of silkworms against various climatic stress conditions, including thermal stresses, oxidative stresses and cold stress has been discussed to give a comprehensive view on the different molecular strategies of silkworm to combat various external stimulus. Heat Shock Proteins (HSPs) are mainly focussed in this adaptation, which acts as crucial molecular chaperones to prevent protein degradation. Heat stress response in silkworms shows higher production of HSPs like HSP70, HSP90, small-HSPs, BmmHSP20.1 etc., which mitigate protein damage and therefore promote thermotolerance. Oxidative stresses are also provoked by high a temperature, which drives the excess production of Reactive Oxygen Species (ROS). Silkworms defend themselves against this threat through a series of coordinated response of antioxidant defence enzyme production like Superoxide Dismutase (SOD), Glutathione S-transferase (GST) and Catalase (CAT). The heat-humidity stress response in silkworm triggers DNA methylation and 20E signalling pathway, which acts against these environment stressors, mediates autophagy and can help identify important resistance genes under stress conditions. Sophisticated cold stress responses are also visible in silkworm breeds that are susceptible to cold. Silkworms demonstrate complete resistance to short-term cold stress, maintaining a 100% survival rate after being exposed to 0°C for up to 12 hours. Ultimately securing a sustainable future of sericulture requires strategic approaches to unify advanced climate-resilient breeding tools like genome editing and SCAR markers to develop robust strains; and simultaneously implementing climate-smart management approaches like temperature control, water efficient host plant cultivation, disease control etc.