20-hydroxyecdysone regulated exosomal transport of mulberry urease drives nitrogen recycling and silkworm development

The recycling of urea nitrogenous by urease presents a valuable approach for optimizing nitrogen utilization in organisms with limited nitrogen resources. In silkworms, haemolymph urea concentration correlates with urease activity, and the urease is derived from their exclusive food source, mulberry leaves. Although mulberry-derived urease has been shown to cross the silkworm midgut barrier, the mechanism of its translocation into the haemolymph remains unknown. In the present study, we investigated the transport mechanism of mulberry urease into the silkworm haemolymph using Western blotting and immunoelectron microscopy. Our results revealed that exosomes and autophagy-related factors, which are regulated by 20-hydroxyecdysone (20E), mediate the stage-specific transport of mulberry urease from the midgut to the haemolymph in silkworm larvae. Urease deficiency impaired silkworm growth and development, significantly reducing cocoon shell weight and egg production. These findings highlight the profound influence of host plants on insect phenotypic traits and reveal a novel cross-kingdom molecular transport mechanism. Our results not only deepen the understanding of plant-insect interactions but also offer practical insights for sericulture improvement, particularly in formulating artificial diets to enhance silk production.