Plant hormones (Literature sources on phytohormones and plant signalling)

Physiologia Plantarum (2023)

Highlights: • Melatonin acts as a redox network regulator in plants via regulating secondary messengers signaling. • Melatonin regulates the activity of redox-sensitive proteins and transcription factors. • Melatonin influences gene expression and physiological processes in response to stresses. • Melatonin synergically work with other hormones to confer plant resistance and stress adaptability. 

Abstract: "Plants being sessile in nature, are exposed to unwarranted threats as a result of constantly changing environmental conditions. These adverse factors can have negative impacts on their growth, development, and yield. Hormones are key signaling molecules enabling cells to respond rapidly to different external and internal stimuli. In plants, melatonin (MT) plays a critical role in the integration of various environmental signals and activation of stress-response networks to develop defense mechanisms and plant resilience. Additionally, melatonin can tackle the stress-induced alteration of cellular redox equilibrium by regulating the expression of redox homeostasis-related genes and proteins. The purpose of this article is to compile and summarize the scientific research pertaining to MT's effects on plants' resilience to biotic and abiotic stresses. Here, we have summarized that MT exerts a synergistic effect with other phytohormones, for instance, ethylene, jasmonic acid, and salicylic acid, and activates plant defense-related genes against phytopathogens. Furthermore, MT interacts with secondary messengers like Ca2+, nitric oxide, and reactive oxygen species to regulate the redox network. This interaction triggers different transcription factors to alleviate stress-related responses in plants. Hence, the critical synergic role of MT with diverse plant hormones and secondary messengers demonstrates phytomelatonin's importance in influencing multiple mechanisms to contribute to plant resilience against harsh environmental factors."

New Phytologist (2022)

Abstract: "Nitric oxide (NO) is known to modulate the action of several phytohormones. This includes the gaseous hormone ethylene, but the molecular mechanisms underlying the effect of NO on ethylene biosynthesis are unclear. Here, we observed a decrease in endogenous NO abundance during apple (Malus domestica) fruit development and exogenous treatment of apple fruit with a NO donor suppressed ethylene production, suggesting that NO is a ripening suppressor. Expression of the transcription factor MdERF5 was activated by NO donor treatment. NO induced the nucleocytoplasmic shuttling of MdERF5 by modulating its interaction with the protein phosphatase, MdPP2C57. MdPP2C57 induced dephosphorylation of MdERF5 at Ser260 is sufficient to promote nuclear export of MdERF5. As a consequence of this export, MdERF5 proteins in the cytoplasm interacted with and suppressed the activity of MdACO1, an enzyme that converts 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. The NO-activated MdERF5 was observed to increase in abundance in the nucleus and bind to the promoter of the ACC synthase gene MdACS1 and directly suppress its transcription."