Preliminary observations on the role of Sirtuin genes in grapevine (Vitis vinifera L.) Physiology

The sirtuin/Sir2 (Silent information regulator 2) family of NAD+-dependent deacetylases and mono-ADP-ribosyltransferases plays a part in several cellular processes including gene silencing, cell cycle regulation and life span extension in yeast and animals. However, information about their occurrence and role in the plant genomes is scarce. Recently, two putative sirtuin genes encoding a SIRT4-like and a SIRT7-like protein respectively were identified in the grapevine genome. Starting from the putative coding sequences present in the database, we have been able to obtain two long fragments of the true coding sequences for each sirtuin gene. In order to better understand the physiological role of both sirtuins, in vitro assays were carried out. We could demonstrate only very weak NAD+-dependent deacetylase activity in vitro, either in the absence or the presence of resveratrol, a naturally occurring phytoalexin which is synthesized in stressed grapevine cells and which is able to activate sirtuins in several organisms. Moreover we did not observe mono- ADP-ribosyltransferase activity in either of the proteins. Finally, we investigated the expression of both sirtuin genes under conditions of stress, such as in the presence methyl jasmonate and UV-C irradiation. Our preliminary assays showed that neither methyl jasmonate nor UV-C rays influence the expression of these grapevine sirtuin genes.