Analysis of the sirtuin genes in Arabidopsis thaliana

Members of the silent information regulator (SIR2) gene family, named sirtuins, are highly conserved, ranging from archeabacteria to eukaryotes. The sirtuin protein functions as a NADdependent deacetylase and mediates silencing by regulating histone acetylation. Phylogenetically, these deacetylases are divided in five classes, based on sequence motifs within their highly corserved Sir2 domain. In Arabidopsis thaliana there are two sirtuin genes, SRT1 and SRT2, belonging respectively to class IV and II. They are very close to human sirtuins SIRT6 and SIRT 4. In the last year, sirtuins from several species, including human, have emerged as important regulators of metabolism, defense and ageing. To evaluate the role of sirtuins in Arabidopsis in this report we will present a first molecular characterisation of these genes. The expression level of SRT1 and SRT2 monitored by semiquantitative RTPCR on the different plant organs examined shows ubiquitous activity but different gene specific pattern. Moreover we have identified and selected mutant plants for each gene, obtained by T-DNA insertional technique and the effect on plant growth has been evaluated under controlled growth condition. An important peculiarity of these enzymes is their susceptibility to inhibition or activation by small molecules. This gives the possibility to have chemical tools to modulate their activity. In particular, resveratrol, a sirtuin activator, is a stilbene produced by few plants and involved in defense response. As Arabidopsis is not able to synthetize this compound, we constructed plants overespressing stilbene synthase, the only key enzyme necessary to produce resveratrol in all plants. Preliminary data of sirtuin gene activity in these trangenic plants show a decreased level of expression of SRT2 gene in young plantelets. Furthermore, investigations on expression patterns and morphological parameters in the presence of different contexts, i.e. specific inhibitors as sirtinol and nicotinammide, known to interfere with their activity, are currently underway.