TmKayak functions as an effector of Jun N-terminal kinase pathway to modulate immune responses in Tenebrio molitor

The c-Jun N-terminal kinase (JNK) signaling pathway plays a critical role in insect stress responses and immunity; however, its downstream transcriptional mechanisms remain poorly understood in coleopteran species. The kayak gene, a Fos homolog that functions as a JNK-responsive transcription factor, has been well studied in Drosophila melanogaster, but its role in beetles remains unexplored. In this study, we examined the functional role of TmKayak in the immune response of Tenebrio molitor using RNA interference. Upon TmKayak knockdown, we assessed the expression patterns of 15 antimicrobial peptide (AMP) genes in four immune-relevant tissues including fat body, gut, Malpighian tubules, and integument following three distinct microorganisms injection with Escherichia coli, Staphylococcus aureus, or Candida albicans. In all three injection models, E. coli, S. aureus, and C. albicans, a noticeable reduction in viability was observed in larvae injected with dsTmkayak compared to the dsEGFP control group. Notably, quantitative real-time PCR analysis revealed that TmKayak knockdown resulted in broad suppression of AMP expression, particularly in response to E. coli and S. aureus. In contrast, a relatively mild regulatory effect was observed following injection with C. albicans. Collectively, these findings identify TmKayak as a key transcriptional effector of the JNK pathway and contribute to a deeper understanding of innate immune regulation in T. molitor.