Survival to cold stress in insects living in temperate environments requires the deployment of strategies that lead to physiological changes involved in freeze tolerance or freeze avoidance. These strategies may consist of, for instance, the induction of metabolic depression, accumulation of cryoprotectants, or the production of antifreeze proteins, however, little is known about the way such mechanisms are regulated and the signals involved in their activation. Ascarosides are signaling molecules usually known to regulate nematode behavior and development, whose expression was recently found to relate to thermal plasticity in the Japanese pine sawyer beetle Monochamus alternatus. Accumulating evidence also points to miRNAs as another class of regulators differentially expressed in response to cold stress, which are predicted to target genes involved in cold adaptation of insects. Here, we demonstrate a novel pathway involved in insect cold acclimation, through miRNA-mediated regulation of ascaroside function. We initially discovered that experimental cold acclimation can enhance the beetle’s cold hardiness. Through screening and functional verification, we found miR-31-5p, upregulated under cold stress, significantly contributes to this enhancement. Mechanistically, miR-31-5p promotes production of an ascaroside (asc-C9) in the beetle by negatively targeting the rate-limiting enzyme, acyl-CoA oxidase in peroxisomal β-oxidation cycles. Feeding experiments with synthetic asc-C9 suggests it may serve as a signal to promote cold acclimation through metabolic depression and accumulation of cryoprotectants with specific gene expression patterns. Our results point to important roles of miRNA-mediated regulation of ascaroside function in insect cold adaptation. This enhanced cold tolerance may allow higher survival of M. alternatus in winter and be pivotal in shaping its wide distribution range, greatly expanding the threat of pine wilt disease, and thus can also inspire the development of ascaroside-based pest management strategies.

中文翻译：

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miR-31-5p通过a虫苷信号传导调节无聊的甲虫Monochamus alternatus的冷驯化

要在温带环境中的昆虫中生存于寒冷胁迫下，就需要采取能够导致生理变化的策略，这些生理变化涉及耐冻性或避免冻害。这些策略可能包括，例如，诱导代谢抑制，冷冻保护剂的积累或抗冻蛋白的产生，但是，对这种机制的调控方式及其激活所涉及的信号知之甚少。scar虫病是通常已知的调节线虫行为和发育的信号分子，最近发现其表达与日本松木锯手甲虫Monochamus alternatus的热可塑性有关。越来越多的证据也表明，miRNA是另一类调节因子，可响应冷应激而差异表达，预计将靶向与昆虫冷适应有关的基因。在这里，我们展示了一种通过miRNA介导的scar虫苷功能调节参与昆虫冷驯化的新途径。我们最初发现实验性冷适应可以增强甲虫的抗寒性。通过筛选和功能验证，我们发现在冷胁迫下上调的miR-31-5p显着促进了这种增强。从机理上讲，miR-31-5p通过在过氧化物酶体β-氧化循环中负向限速酶酰基辅酶A氧化酶来促进甲虫中scar螨苷（asc-C9）的产生。饲喂合成asc-C9的实验表明，它可能是通过代谢抑制和具有特定基因表达模式的冷冻保护剂积累促进冷驯化的信号。我们的研究结果表明miRNA介导的scar虫苷功能调节在昆虫冷适应中的重要作用。这种增强的耐寒性可以使互生分枝杆菌在冬季有更高的生存率，并且在改变其广泛分布范围方面起着关键作用，极大地扩大了松树枯萎病的威胁，因此也可以激发基于a虫苷的害虫治理策略的发展。