Photo-enzymatic repair of UVB-induced DNA damage in the two-spotted spider mite Tetranychus urticae.

Ambient ultraviolet-B (UVB) radiation induces lethal effects in the two-spotted spider mite Tetranychus urticae, whereas photoreactivation by irradiation with ultraviolet-A and visible light (VIS) plays an important role to increase survival of mites irradiated by UVB. The physiological mechanisms and ecological significance of photoreactivation in terrestrial arthropods have not been shown clearly. We verified the biological impact and accumulation of DNA lesions by UVB irradiation and the repair of them by photoreactivation in T. urticae larvae. Survival of UVB-irradiated larvae decreased with increasing UVB dose, but recovered remarkably with VIS exposure after UVB irradiation (photoreactivation). The DNA lesions, cyclobutane pyrimidine dimers (CPDs) and 6-4 pyrimidine-pyrimidine photoproducts (6-4PPs) linearly increased with the UVB dose. The CPDs were repaired after exposure to VIS, whereas the frequency of 6-4PPs was unaffected by VIS; CPD photolyase genes, but not (6-4) photolyase genes, have been found in the T. urticae genome. Therefore, DNA damage and CPD photo enzymatic repair (PER) is significant for survival in this mite under ambient UVB radiation. Unexpectedly, gene expression of CPD photolyase was unaffected by irradiation with UVB and VIS. Instead, expression of xeroderma pigmentosum A (XPA) was increased by irradiation. XPA is a core factor in nucleotide excision repair (NER), which is a repair system unrelated to photo energy. The relationship between gene expression and enzymatic repair remains unclear. To elucidate the PER process in T. urticae, further study will be necessary on the gene expression patterns and molecular functions of CPD photolyase in PER and of XPA in NER.