Illuminating Ultraviolet-C on Plants: Insights into Mechanism, Regulation and Response

Ultraviolet-C (UV-C) radiation has emerged as a potent artificial light signal capable of triggering complex molecular responses in plants. Unlike ultraviolet-A (UV-A) and ultraviolet-B (UV-B), for which specific photoreceptors and signalling pathways are well characterised, the molecular mechanisms underlying UV-C perception and signalling remain largely unexplored. Recent evidence indicates the involvement of early signalling events, including the generation of reactive oxygen species (ROS), ion fluxes, activation of mitogen-activated protein kinase (MAPK) cascades and hormonal signalling. These signals drive transcriptional reprogramming through key transcription factors such as WRKY transcription factor (WRKY), v-Myb myeloblastosis viral oncogene homolog (MYB), Ethylene Responsive Factor (ERF), Heat Shock Factor (HSF) and Lateral Organ Boundaries Domain (LBD), along with post-transcriptional regulation by microRNAs like miR398 and miR159. The resulting gene expression changes modulate defence responses, hormone signalling, secondary metabolism, and cell wall modification, with considerable variation across species and cultivars. These molecular changes are also associated with morphological and physiological responses, including effects on plant growth, stress adaptation, fruit ripening and colouration. This review integrates emerging evidence on UV-C perception, signalling networks, and transcriptional regulation within a mechanistic framework, presented schematically to offer a holistic view of how UV-C shapes plant morphology, physiology, biochemistry and identifies critical gaps in photoreceptor identification, kinase signalling, and miRNA-mediated regulation. Collectively, these insights establish a foundation for the development of UV-C-based strategies to enhance crop resilience, nutritional quality, and stress tolerance in a sustainable and precise manner.