Improvement of abiotic stress tolerance by modulating polyamine pathway in crop plants

Various abiotic stresses severely affect crop plant germination, growth, and productivity worldwide. Plants exhibit numerous mechanisms to battle against hostile abiotic stress. Out of several mechanisms, here we focused on the polyamine metabolic pathway. Polyamines exist in the plants with free or covalently/noncovalently conjugated forms and mainly three types, i.e., putrescine, spermidine, and spermine. These are involved in various cellular processes such as DNA replication, transcription, cell membrane stability, cell division, regulation of enzyme activity, and in abiotic stress, etc. Polyamines biosynthesis pathways in plants use two critical precursor substrates, i.e., L-arginine and methionine. In the present chapter, we will focus on genes and enzymes involved in polyamines biosynthetic and catabolism. Multiple functional roles of polyamines at the cellular level and during the developmental stage, during high-temperature stress, during cold and chilling stress, during water and drought stress are discussed in detail. Apart from these, we also focused on genetic engineering in polyamines pathways to develop abiotic stress-tolerant crops. Genetic manipulation using plant genetic engineering tools by targeting ADC, ODC, SPDS, SAM, and SAMDC in different plants improved abiotic stress tolerance. Apart from these genes, transcription factors regulating these pathways need to be explored to achieve better abiotic stress-tolerant plants.