Involvement of Arabidopsis thaliana ribosomal protein S27 in mRNA degradation triggered by genotoxic stress

A recessive Arabinopsis mutant with elevated sensitivity to DNA damaging tr eatments was identified in one out of 800 families generated by T-DNA inser tion mutagenesis. The T-DNA generated a chromosomal deletion of 1287 bp in the promoter of one of three S27 ribosomal protein genes (ARS27A) preventin g its expression, Seedlings of ars27A developed normally under standard gro wth conditions, suggesting wild-type proficiency of translation, However, g rowth was strongly inhibited in media supplemented with methyl methane sulf ate (MMS) at a concentration not affecting the wild type. This inhibition w as accompanied by the formation of tumor-like structures instead of auxilia ry roots. Wild-type seedlings treated with increasing concentrations of MMS up to a lethal dose never displayed such a trait, neither was this phenoty pe observed in ars27A plants in the absence of MMS or under other stress co nditions. Thus, the hypersensitivity and tumorous growth are mutant-specifi c responses to the genotoxic MMS treatment. Another important feature of th e mutant is its inability to perform rapid degradation of transcripts after UV treatment, as seen in wild-type plants. Therefore, we propose that the ARS27A protein is dispensable for protein synthesis under standard conditio ns but is required for the elimination of possibly damaged mRNA after UV ir radiation.