Photolyase genes and light-dependent DNA repair during embryogenesis of freshwater prawns under ultraviolet-B radiation stress.

Ultraviolet-B (UVB) radiation is an important abiotic factor that, at high intensities, acts as an environmental stressor, inducing DNA damage (e.g. cyclobutane pyrimidine dimers (CPD), and 6-4 photoproducts), which compromise genomic integrity if unrepaired. Aquatic embryos developing in shallow waters are particularly vulnerable to UVB, which can impair development and increase long-term damage. To counteract UVB-induced effects, many organisms rely on photoreactivation, a light-dependent DNA repair mediated by photolyases. However, the diversity, regulation, and functional activity of photolyases in freshwater crustaceans remain poorly understood. We investigated the molecular and functional basis of DNA photorepair in embryos of the prawn Macrobrachium olfersii, a species naturally exposed to high solar UVB radiation. In silico analyses identified two photolyase genes (phr1 and phr2), both containing conserved DNA_photolyase and FAD_binding_7 domains. Phylogenetic analysis placed both genes within class II CPD photolyases. Gene expression analyses during embryogenesis (E3-E10) and in adult tissues revealed transcription throughout embryonic development and restricted expression in ovaries and the cerebral ganglion in adults. Although no temporal modulation of photolyase expression was observed following UVB exposure in E7 embryos, environmentally collected embryos displayed increased basal phr1 levels, and higher UVB doses under laboratory conditions significantly induced both genes. Functional assays demonstrated that protein extracts from environmental embryos repaired UV-induced DNA damage in a light-dependent manner, providing evidence of photoreactivation in M. olfersii. Collectively, these findings demonstrate the presence and functional relevance of photolyase-mediated DNA repair during crustacean embryogenesis and highlight its ecological significance under scenarios of increased UVB exposure associated with global climate change.