A Mutation in gene, which promotes the progression of endoreduplication, confers an increased tolerance against UV-B light

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

We have isolated and characterized an ultraviolet-B resistant mutant, uvi4, of Arabidopsis. The fresh weight of uvi4 plants grown under supplemental UV-B light was more than twice of that of the wild type. No significant difference was found in the ability to repair the UV-B-induced cyclobutane pyrimidine dimmers 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 UVI4 gene encodes a novel basic protein of unknown function. The UVI4 gene is expressed mainly in actively dividing cells. We found that the hypocotyls cells in uvi4 undergo one extra round of endoreduplication. The uvi4 mutation also promoted the progression of endoreduplication during leaf development. Tetraploid Arabidopsis was hyperresistant to UV-B than diploid Arabidopsis. These results suggest that the enhanced polyploidization is responsible for the increased UV-B tolerance of the uvi4.