A Mutation in the gene promotes progression of endo-reduplication and confers increased tolerance towards ultraviolet B light

Hase, Yoshihiro; Trung, K. H.*; Matsunaga, Tsukasa*; Tanaka, Atsushi

We have isolated and characterized a new ultraviolet-B (UV-B)-resistant mutant, , of Arabidopsis. The fresh weight of plants grown under supplemental UV-B light was more than twice that of the wild type. No significant difference was found in the ability to repair the UV-B-induced cyclobutane pyrimidine dimers (CPDs), or in the amount of UV-B absorptive compounds, both of which are well known factors that contribute to UV sensitivity. Positional cloning revealed that the gene encodes a novel basic protein of unknown function. We found that the hypocotyl cells in undergo one extra round of endoreduplication. The mutation also promoted the progression of endoreduplication during leaf development. The gene is expressed mainly in actively dividing cells. In the leaves of P::GUS plants, the GUS signal disappeared in basipetal fashion as the leaf developed. The total leaf blade area was not different between and the wild type through leaf development, while the average cell area in the adaxial epidermis was considerably larger in , suggesting that the leaves have fewer but larger epidermal cells. These results suggest that the is necessary for the maintenance of the mitotic state and the loss of function stimulated endoreduplication. Tetraploid Arabidopsis was hyperresistant to UV-B compared to diploid Arabidopsis, suggesting that the enhanced polyploidization is responsible for the increased UV-B tolerance of the .