Polyamines: Emerging Hubs Promoting Drought and Salt Stress Tolerance in Plants

Abstract

Environmental stress is increasingly wearing down crop productivity. As a consequence, a major priority of plant research is to get deeper insights on tolerance mechanisms, providing solutions with the generation of stress-tolerant cultivars. To this goal, a common target of genetic modification is the polyamine signaling pathway. Its association with a protective role against stressful stimuli is widely acknowledged; however, the nature of this function is highly complex. In consequence, this review aims to present up-to-date evidence in regard with metabolic and physiological role of polyamines, protecting plants during severe stressful events (such as drought and soil salinization). The most recent evidence from stress physiology research highlight polyamines as key players in signaling responses involved in central metabolism, sugar and lipid homeostasis, maintenance, and induction of antioxidant capacity as well as osmotic regulation. Nevertheless, a number of questions remain open, such as the extent of their roles and whether they represent hub metabolic molecules. Recent advances on polyamine metabolism are therefore summarized in relation to salt and drought stress tolerance and its possible implication on the generation of tolerant crops. This review highlights recent findings related to polyamine protective role during drought and salt stress. A clear synergy is established between these amine compounds, ABA, and reactive oxygen and nitrogen species. However, the involvement of these amine compounds on stress physiology goes far beyond the modulation of nitro-oxidative homeostasis and ABA signaling, with an increasing body of evidence demonstrating that polyamines are emerging metabolic hubs of plant stress signaling.