det1-1-induced UV-C hyposensitivity through UVR3 and PHR1 photolyase gene over-expression.

Obligate photoautotrophs such as plants must capture energy from sunlight and are therefore exposed to the damaging collateral effects of ultraviolet (UV) irradiation, especially on DNA. Here we investigated the interconnection between light signaling and DNA repair, two concomitant pathways during photomorphogenesis, the developmental transition associated with the first light exposure. It is shown that combination of an enhanced sunscreen effect and photoreactivation confers a greater level of tolerance to damaging UV-C doses in the constitutive photomorphogenic de-etiolated1-1 (det1--1) Arabidopsis mutant. In darkness, expression of the PHR1 and UVR3 photolyase genes, responsible for photoreactivation, is maintained at a basal level through the positive action of HY5 and HYH photomorphogenesis-promoting transcription factors and the repressive effects of DET1 and COP1. Upon light exposure, HY5 and HYH activate PHR1 gene expression while the constitutively expressed nuclear-localized DET1 protein exerts a strong inhibitory effect. Altogether, the data presented indicate a dual role for DET1 in controlling expression of light-responsive and DNA repair genes, and describe more precisely the contribution of photomorphogenic regulators in the control of light-dependent DNA repair.