Nutrition-dependent juvenile hormone sensitivity promotes flight-muscle degeneration during the aphid dispersal-reproduction transition.

Abstract

In insects, the loss of flight typically involves a dispersal-reproduction transition, but the underlying molecular mechanisms remain poorly understood. In the parthenogenetic pea aphid Acyrthosiphon pisum, winged females undergo flight-muscle degeneration after flight and feeding on new host plants. Similarly, topical application of a juvenile hormone (JH) mimic to starved aphids also induces flight-muscle degeneration. We found that feeding preferentially upregulated the expression of the JH receptor gene Met and a JH-inducible gene, Kr-h1, in the flight muscles, and, thus, enhanced tissue-specific JH sensitivity and signaling. RNAi-mediated knockdown of Kr-h1 prevented flight-muscle degeneration. Likewise, blocking nutritional signals by pharmacological inhibition of the target of rapamycin complex 1 (TORC1) impaired JH sensitivity of the flight muscles in feeding aphids and subsequently delayed muscle degeneration. RNA-sequencing analysis revealed that enhanced JH signaling inhibited the transcription of genes involved in the tricarboxylic acid cycle, likely resulting in reduction of the energy supply, mitochondrial dysfunction and muscle-fiber breakdown. This study shows that nutrient-dependent hormone sensitivity regulates developmental plasticity in a tissue-specific manner, emphasizing a relatively underappreciated mechanism of hormone sensitivity in modulating hormone signaling.