Influence of UV-light on the expression of the Cat2 and Cat3 catalase genes in maize.

The effects of UV (ultraviolet) -irradiation on the expression of the antioxidant genes Cat2 and Cat3, encoding the CAT-2 and CAT-3 catalases in maize were examined. Cat2 and Cat3 transcript accumulation was analyzed in leaves of maize seedlings grown under different light conditions, and subsequently exposed to UV-light. Under DD-(constant darkness) and LL- (continuous light) conditions, as well as under a 12h D/L- (dark/light) photoperiod, the Cat2 mRNA was expressed at low and constant levels. In contrast, Cat3 transcript accumulation was constant and about 10 times higher than that of Cat2 under DD or LL, while the expression of Cat3 exhibits a typical circadian rhythm under a 12h D/L photoperiod. UV- light pulses in the range of 290 to 400 nm strongly induce the expression of Cat2. Upon removing the UV-B portion (290-310 nm) of the UV-spectrum the maximal Cat2 transcript level was reduced by about 60%. On applying UV-light of the same quality in addition to visible light, the expression of Cat2 was induced. DNA damage caused by UV-light and induction mediated by a UV-light photosensory system are suggested. Further, it is suggested that the Cat3 circadian rhythm may be regulated by a blue light/UV-A and a UV-B photoreceptor. If DD and LL grown plants that exhibit no circadian oscillation, were exposed to constant UV-light in the range of 290 to 400 nm a circadian rhythm was induced; indicating that UV-light may function as an additional environmental cue to entrain the Cat3 circadian rhythm. Since, Cat2 and Cat3 showed distinct responses to UV light, it is suggested that both genes may act to scavenge reactive oxygen species (ROS) generated by UV-light to protect the plant from oxidative damage.