A Functional Study of Arabidopsis thaliana Sirtuins

Abiotic stresses are major causes of yield loss in cultivated crops. These losses are the result of multiple mild stresses episodes throughout the growing season as well as periodical severe stresses. Breeding of crop varieties with improved responses to environmental changes is an important goal in modern agriculture. Crop varieties with enhanced tolerance to abiotic stress will broaden the window of optimal growth conditions for cultivated crops, thereby increasing average yield, yield stability and productive acreage. Such traits will provide substantial benefits to farmers and processors and may reduce costs in seed production. Today the molecular and biochemical mechanisms involved in abiotic stress responses are still poorly understood and the signaling networks remain elusive. Recent data indicate that an efficient energy homeostasis contributes to stress tolerance and that the modulation of cellular NAD(P) homeostasis is an attractive and innovative strategy to improve plant performance in stress conditions. Functional studies in various eukaryotes indicate a potential important role for sirtuins in NAD⁺ dependent stress tolerance. Sirtuins catalyze protein and histone deacetylation and play a role in metabolic regulation and ageing. The Arabidopsis genome contains two SIRTUIN genes that are classified as type III deacetylases. AtSIR2 transcripts are detected as 7 different splice forms, allowing a dual targeting to nuclei and mitochondria. Stress-related phenotyping of loss-and-gain of function transgenic lines demonstrated a crucial role for both genes in maintaining proficient growth characteristics during oxidative and salt-stress conditions. Through genome-wide transcriptome profiling experiments, we could reveal that downregulation of AtSIR2 abolishes a specific part of the salt stress response that is most likely responsible for the observed phenotypes. An interactome study using tandem affinity purification indicates that AtSIRs interact with chromating remodelling factors in the nucleus and are responsible for the deacetylation of histones, subunits of the  mitochondrial respiratory complex and cytosolic proteins.