Age-associated alterations in the somatic mutation level in Arabidopsis thaliana

Age-related accumulation of somatic mutations has been implicated as an important mechanism contributing to ageing and various diseases in animals. However, it is unclear whether the somatic mutation frequency changes as plants age and to what extent somatic mutagenesis contributes to plant ageing or senescence. The contribution of somatic mutagenesis to plant ageing and senescence was not investigated. We used the species Arabidopsis thaliana to study whether an increasing chronological age of an annual plant species influences the total amount and molecular spectrum of somatic DNA mutations. The number of small-scale somatic mutations was studied in nine randomly chosen A. thaliana control DNA regions, including those in the nuclear genome (Actin2 coding region, Actin2 3′-UTR region, CMT3 methyltrasferase gene, tRNAPro, and ITS1-5.8rRNA-ITS2), mitochondrial DNA (cytochrome oxidase C, a gene encoding an unnamed protein, and a noncoding mitochondrial DNA region), and chloroplast DNA (rbcL gene). We found that the frequency of single nucleotide substitutions, insertions, and deletions increased considerably during the A. thaliana growth and development from the seeds to the 12-week-old plants. The vast majority of nucleotide substitutions (~86 %) were transitions with A:T→G:C transitions being the most frequent type of substitution. The data indicate that at least some plant DNA regions accumulate point mutations during plant aging.