Abstract
UVB radiation can damage DNA by causing formation of cyclobutane pyrimidine dimer (CPD). Photoreactivation mediated by an enzyme, photolyase, is the major pathway for repairing CPD in plants. We previously reported that the different degrees of UVB sensitivity in rice are caused by mutations in the CPD photolyase gene, and CPD photolyase activity plays an important role in preventing UVB-caused growth inhibition. However, it is poorly understood the characteristics and functions of CPD photolyase in plant. We present two topics about the CPD photolyase in rice as mentioned below.
(1)Characterization of CPD photolyase from rice plant. Native CPD photolyase was purified from rice leaves by anion exchange and heparin affinity chromatography. At final step, enzyme was bound to CPD-containing DNA conjugated to magnetic beads and released by blue irradiation, with an overall increase in specific activity of about 8,000-fold. SDS-PAGE and western blotting analyses indicated that native rice photolyase contains of two 54- and 56-kDa isoforms. The purified native enzyme activity was much higher than enzyme expressed in E. coli.
(2)CPD photolyase encoded by a single-copy gene in nuclei functions in nuclei, chloroplast and mitochondria in rice plant. We found that UVB-induced CPD on not only nuclei but also chloroplast and mitochondrial genome was repaired dependently by exposure of blue irradiation in rice. Furthermore, the CPD photoreactivation in each organelle was not detected in antisense transgenic plant with little CPD photolyase activity.
