Anthocyanins are key regulators of drought stress tolerance in tobacco

Simple Summary: Water scarcity is one of the main threats for the future of agriculture and the worldwide population. Improving the ability of crop species to grow and survive with less water is therefore essential. A fundamental goal of most scientists working in this area is to understand the mechanisms plants must potentiate to better survive under reduced water availability. Here we provide evidence that accumulation of anthocyanins, a major player in red leaf color, may fulfil two important functions. First, they serve as a filter for protecting plants against excessive sunlight; second, they control plant water loss by reducing stomatal transpiration and density. Since excessive sunlight and temperature, associated with climate change, come along with water shortage, these pigments may protect and help plants to survive throughout hot and dry seasons. Our results have important social implications for people living in areas where rising temperatures and water shortages are already critical. Breeding programs to obtain crops with these stress tolerance traits can be specifically designed for these environments. Abiotic stresses will be one of the major challenges for worldwide food supply in the near future. Therefore, it is important to understand the physiological mechanisms that mediate plant responses to abiotic stresses. When subjected to UV, salinity or drought stress, plants accumulate specialized metabolites that are often correlated with their ability to cope with the stress. Among them, anthocyanins are the most studied intermediates of the phenylpropanoid pathway. However, their role in plant response to abiotic stresses is still under discussion. To better understand the effects of anthocyanins on plant physiology and morphogenesis, and their implications on drought stress tolerance, we used transgenic tobacco plants (AN1), which over-accumulated anthocyanins in all tissues. AN1 plants showed an altered phenotype in terms of leaf gas exchanges, leaf morphology, anatomy and metabolic profile, which conferred them with a higher drought tolerance compared to the wild-type plants. These results provide important insights for understanding the functional reason for anthocyanin accumulation in plants under stress.