Role of AtPolζ, AtRev1 and AtPolη in γ ray-induced mutagenesis.

Although ionizing radiation has been employed as a mutagenic agent in plants, the molecular mechanism(s) of the mutagenesis is poorly understood. AtPolζ, AtRev1 and AtPolη are Arabidopsis translesion synthesis (TLS)-type polymerases involved in UV-induced mutagenesis. To investigate the role of TLS-type DNA polymerases in radiation-induced mutagenesis, we analyzed the mutation frequency in AtPolζ-, AtRev1- or AtPolη-knockout plants rev3-1, rev1-1 and polh-1, respectively. The change in mutation frequency in rev3-1 was negligible, whereas that in rev1-1 decreased markedly and that in polh-1 increased slightly compared to wild-type. Abasic (apurinic/apyrimidinic; AP) sites, induced by radiation or generated during DNA repair processes, can pair with any kind of nucleotide on the opposite strand. 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG), induced by radiation following formation of reactive oxygen species, can pair with cytosine or adenine. Therefore, AtRev1 possibly inserts dC opposite an AP site or 8-oxo-dG, which results in G to T transversions.