The Arabidopsis thaliana SIRT2 sirtuin is involved in DNA damage response

Sirtuins, NAD-dependent deacetylases, are present in all organisms playing a central role in many metabolic pathways such as cell survival, energy metabolism, lifespan and ageing. Among the seven human sirtuins, SIRT4 and SIRT6 share conserved domains with the two sirtuins present in the flowering plant Arabidopsis thaliana, named SRT1 and SRT2. In particular SRT1 has sequence homology to nuclear SIRT6 while SRT2 to mithochondrial SIRT4. Several roles for SIRT4 are known but recently its engagement in DNA Damage Response (DDR) has been proposed. Among metabolic pathways that limit proliferation under damage, the repression of glutamine metabolism has been demonstrated. In human cells, the transcriptional activation of Sirt4 gene, in response to DNA-damaging agents, inhibits both glutamine entry into the cells and glutamate dehydrogenase (GDH) activity, decreasing the production of tricarboxylic acid cycle intermediates and reducing energy for proliferation (Jeong et al, 2013). Few and contrasting data are until now available on plant SRT2. A lysine deacetylase activity and an involvement in energy metabolism and pathogen defense have been reported for this sirtuin. In a project to search for equivalent functions of conserved genes deriving from phylogenetically distant organisms, here we present an analysis to verify if SRT2 displays in plant the same role observed for SIRT4 in human cells. We have evidenced by informatic programmes that the two sirtuins SIRT4 and SRT2 share not only aminoacid sequence but also tridimensional structure. Then we have developed an in vivo assay in Arabidopsis to monitor SRT2 expression, cell proliferation and viability, and to evaluate glutamine metabolism. We demonstrate, in Arabidopsis seedlings, after a DNA damage treatment with camptothecin (CPT), a topoisomerase 1 inhibitor, a time and dose-dependent transcriptional activation of SRT2 gene. In parallel, we observe an inhibited cell proliferation and a decreased GDH activity. These data suggest that SRT2 is not only activated in the DDR, but it is also implicated in the glutamine regulation. The same parameters will be evaluated in the selected SRT2 mutant plants obtained by TDNA insertional technique.