Deciphering UV-C-induced transcriptomic shifts in tomato: defence mechanisms, stress responses, and photoreceptor regulation.

Key message: This study reveals transcriptomic reprogramming in tomato under UV-C, highlighting enriched defence pathways, calcium signalling, enhanced pathogen tolerance, increased defence enzyme activity, and photoreceptor-mediated UV-C perception, linking light signalling to stress adaptation. UV-C radiation, when applied at hormetic dosage, acts as a mild abiotic stressor in plants, triggering beneficial responses that enhance yield and bioactive compound production. However, transcriptomic responses to UV-C remain underexplored. This study investigates UV-C-induced transcriptomic changes in two tomato cultivars with differing UV-C susceptibility; Red Rock (susceptible) and Super Star (comparatively tolerant). RNA-seq analysis revealed 3540 DEGs in Red Rock and 2678 in Super Star, with a higher proportion of up-regulated genes in both cultivars after UV-C exposure. GO analysis indicated a conserved response, with enriched pathways associated with defence and stress adaptation. KEGG and PGSEA analyses highlighted significant enrichment in phenylpropanoid biosynthesis, plant-pathogen interaction, and fatty acid degradation pathways. Calcium-binding and signalling genes were predominantly up-regulated, suggesting a key role in UV-C-induced defence responses. RT-qPCR analysis of 17 selected genes, in both cultivars, showed the highest change in expression for Solyc06g069740.1, encoding a calcium-binding EF-hand family protein involved in signal transduction and Solyc05g050350.2, a Cyclic nucleotide-gated ion channel 1 involved in ion transport across the membrane during defence response. Detached leaf assays with Botrytis cinerea and Sclerotinia sclerotiorum demonstrated enhanced pathogen tolerance in UV-C-treated plants, with reduced lesion sizes and increased defence enzyme activity, including chitinase, phenylalanine ammonia-lyase, β-1,3-glucanase, and polyphenol oxidase, compared to fungal-treated controls. Further analysis of photoreceptors revealed upregulation of UV Resistance Locus 8 and Cryptochromes, linking UV-C perception to downstream signalling. These findings provide insights into UV-C-induced defence mechanisms and potential applications for improving crop resilience and productivity.