Trr/COMPASS regulates photoperiodic reproductive diapause via 20-hydroxyecdysone signaling in Colaphellus bowringi

Developmental plasticity allows animals to survive harsh conditions. In insects, reproductive diapause is a classic form of plasticity, characterized by ovarian arrest. This process is typically triggered by seasonal cues such as photoperiod and governed by endocrine pathways. However, how photoperiods are converted into endocrine signals that determine reproductive fate remains unclear. The cabbage beetle ( Colaphellus bowringi ) displays a clear photoperiodic response: long-day (LD) conditions induce diapause with ovarian arrest, whereas short-day (SD) conditions promote ovarian development and reproduction. Here, we identified eight conserved subunits of the Trr/COMPASS complex and found their transcriptional levels significantly higher in the ovaries of SD females compared to LD females. Knockdown of Trr/COMPASS components caused ovarian arrest in SD females, accompanied by reduced production and signaling of 20-hydroxyecdysone (20E). We further identified serine/threonine-protein kinase polo ( plk1 ) as a key downstream effector of 20E signaling that promotes ovarian development. Trr/COMPASS-mediated H3K4me3 enrichment was found in regulatory regions of plk1 and several 20E pathway genes, facilitating their transcriptional activation. These findings reveal a photoperiod-sensitive signaling axis, Trr/COMPASS–20E– plk1 , linking environmental cues to endocrine regulation and reproductive diapause, highlighting the essential role of histone modification in developmental adaptation to seasonal changes.