Engineering Polyamine Metabolic Pathways for Abiotic Stress Tolerance in Plants

In the current scenario of climate change, plants are being challenged with frequent episodes of extreme weather events and suffer recurrently from various abiotic stresses that negatively affect growth and development and limit plant productivity. Abiotic stresses activate the expression of several stress-related genes, leading to the synthesis of active proteins and accumulation of metabolites, and other osmotically active compounds. Among these compounds, we can highlight the polyamines (PAs), interesting biomolecules that play an important role on plant physiology, development, and response to environment. PAs are low-molecular-weight, positively charged, aliphatic amines that are found widespread in living organisms. In plants, the most abundant PAs are putrescine (Put), spermidine (Spd), and spermine (Spm). They are synthesized from decarboxylation of amino acids, mainly arginine and ornithine. Put is synthesized primarily through the activity of the enzymes arginine decarboxylase (ADC) and ornithine decarboxylase (ODC). Put is then converted into Spd by spermidine synthase (SPDS), and Spd is further converted into Spm by Spm synthase (SPMS). PA levels in plants increase under a number of environmental stress conditions, including drought, high salinity, and exposure to extreme temperatures (heating or freezing). Numerous studies have provided evidences that enhanced accumulation of PAs in plants is correlated with increased resistance to adverse environmental conditions. In this chapter, we will provide a current state of the art on the works related to the development of plants with altered PA contents, by the manipulation of PA metabolic pathways through genetic engineering, and discussed the possible associated effects on several abiotic stresses.