Unraveling the crosstalk among ethylene, nitric oxide, and polyamines in tailoring the abiotic stress resilience in plants

Abiotic stresses are the major factors affecting the growth and productivity of plants. After perceiving the stress, plants orchestrate sophisticated signaling to maximize their fitness under stress conditions which involves the synthesis or inhibition of various plant growth regulators (PGRs). Among others, ethylene (ET), polyamines (PAs), and nitric oxide (NO) are emerging as crucial PGRs that shape plant responses to various stresses. Interestingly, their biosynthesis is interconnected through common precursors, S-adenosyl methionine (SAM) and L-arginine; therefore, the generation of one affects the synthesis and signaling of the other. Oxidative stress, driven by the production of reactive oxygen species (ROS), is a common feature across all types of stress which triggers several downstream responses such as membrane damage and osmotic imbalance. The troika of ET-PA-NO works in harmony to ensure the maintenance of ROS homeostasis by activating enzymatic and nonenzymatic antioxidants, phytohormones and other PGRs, and several stress-related proteins. Moreover, this trio also tailors various stress-specific responses such as closing stomata under drought and UV-B stress, inducing anaerobic genes during hypoxia, limiting heavy metals uptake by modifying Casparian strip, and maintaining ion/osmotic homeostasis and membrane integrity during salinity and cold stress. In the present review, efforts have been made to present the interconnections among ET-PA-NO as well as their crosstalk in discrete abiotic stresses to unveil and understand their interrelated regulatory mechanisms.