Resistance to UVB radiation in plant

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1. The difference in UVB sensitivity among rice cultivars is caused by a structure/function alteration of photolyase due to one or two amino acids changes, and the CPD photolyase activity is a crucial factor for determining UVB sensitivity in rice.2. Rice plants with higher CPD photolyase activity by overexpressing CPD photolyase gene showed extremely stronger resistance to UVB-caused growth inhibition, whereas rice plants with lower CPD photolyase activity by insertion of antisense CPD photolyase gene showed extremely higher sensitivity to UVB.3. To clarify the function of rice class II CPD photolyase, effects of alterations of deduced amino acids in CPD photolyase on enzyme activity was investigated using rice CPD photolyase expressed in E.coli. Amino acids Gln296, Ser282 and Ser285 functioned as a FAD binding site. On the other hand, W344 and Y419 worked for binding to neither FAD nor CPD, but play an important role in enzyme activity.4. UV-sensitive mutant (rev3-1) and UV-resistant mutant (uvi4) in Arabidopsis were isolated and characterized. 1)Disrupted mutant of AtREV3, a gene for the putative catalytic subunit of Arabidopsis DNA polymerase ζ, was found to be sensitive to UVB and various DNA-damaging agents. 2)Positional cloning revealed that the uvi4 gene encoded a novel basic protein with unknown function. The hypocotyl cells in uvi4 underwent one extra round of endo-reduplication, and the enhanced polyploidization was responsible for the increased UVB tolerance of the uvi4 mutant.5. Three QTLs associated with UVB resistance on chromosomes 1, 3, and 10, using backcross inbred lines were derived from a cross between an indica cultivar "Kasalath" (UV-sensitive) and a japonica cultivar "Nipponbare" (UV-resistant). Among the QTLs, qUVR-10 for UVB resistance was cloned by map-based strategy. The qUVR-10 contained encoded the CPD photolyase gene.