UV-damage-mediated induction of homologous recombination in Arabidopsis isdependent on photosynthetically active radiation

Plants are continuously subjected to UV-B radiation (UV-B; 280-320 nm) as a component of sunlight causing damage to the genome. For elimination of DNA damage, a set of repair mechanisms, mainly photoreactivation, excision, an d recombination repair, has evolved. Whereas photoreactivation and excision repair have been intensely studied during the last few years, recombinatio n repair, its regulation, and its interrelationship with photoreactivation in response to UV-B-induced DNA damage is still poorly understood. In this study, we analyzed somatic homologous recombination in a transgenic Arabido psis line carrying a beta -glucuronidase gene as a recombination marker and in offsprings of crosses of this line with a photolyase deficient uvr2-1 m utant. UV-B radiation stimulated recombination frequencies in a dose-depend ent manner correlating linearly with cyclobutane pyrimidine dimer (CPD) lev els. Genetic deficiency for CPD-specific photoreactivation resulted in a dr astic increase of recombination events, indicating that homologous recombin ation might be directly involved in eliminating CPD damage. UV-B irradiatio n stimulated recombination mainly in the presence of photosynthetic active radiation (400-700 nm) irrespective of photolyase activities. Our results s uggest that UV-B-induced recombination processes may depend on energy suppl y derived from photosynthesis.