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

A recessive Arabidopsis mutant with elevated sensitivity to DNA damaging treatments was identified in one out of 800 families generated by T-DNA insertion mutagenesis. The T-DNA generated a chromosomal deletion of 1287 bp in the promoter of one of three S27 ribosomal protein genes (ARS27A) preventing its expression. Seedlings of ars27A developed normally under standard growth conditions, suggesting wild-type proficiency of translation. However, growth was strongly inhibited in media supplemented with methyl methane sulfate (MMS) at a concentration not affecting the wild type. This inhibition was accompanied by the formation of tumor-like structures instead of auxiliary roots. Wild-type seedlings treated with increasing concentrations of MMS up to a lethal dose never displayed such a trait, neither was this phenotype observed in ars27A plants in the absence of MMS or under other stress conditions. Thus, the hypersensitivity and tumorous growth are mutant-specific responses to the genotoxic MMS treatment. Another important feature of the 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 conditions but is required for the elimination of possibly damaged mRNA after UV irradiation.