The role of phytomelatonin receptor 1-mediated signaling in plant growth and stress response

Abstract

Phytomelatonin is a pleiotropic signaling molecule that regulates plant growth, development, and stress response. In plant cells, phytomelatonin is synthesized from tryptophan via several consecutive steps that are catalyzed by tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acyltransferase (SNAT), and N-acetylserotonin methyltransferase (ASMT) and/or caffeic acid-3-O-methyltransferase (COMT). Recently, the identification of the phytomelatonin receptor PMTR1 in Arabidopsis has been considered a turning point in plant research, with the function and signal of phytomelatonin emerging as a receptor-based regulatory strategy. In addition, PMTR1 homologs have been identified in several plant species and have been found to regulate seed germination and seedling growth, stomatal closure, leaf senescence, and several stress responses. In this article, we review the recent evidence in our understanding of the PMTR1-mediated regulatory pathways in phytomelatonin signaling under environmental stimuli. Based on structural comparison of the melatonin receptor 1 (MT1) in human and PMTR1 homologs, we propose that the similarity in the three-dimensional structure of the melatonin receptors probably represents a convergent evolution of melatonin recognition in different species.

Have All of the Phytohormonal Properties of Melatonin Been Verified?

“…Melatonin is biosynthesized and catabolized like other phytohormones, and its metabolic pathways consist of a regulatory network together with other phytohormones [ 64 ]. Melatonin is synthesized in plants from tryptophan (Trp) mainly via trypamine, serotonin, and N -acetylserotonin [ 66 , 73 ]. However, under some environmental stresses, melatonin is produced via alternative pathways using 5-hydroxytryptophan or 5-methoxytryptophan or both as intermediates.…”

Mechanistic Approach on Melatonin-Induced Hormesis of Photosystem II Function in the Medicinal Plant Mentha spicata

“…Melatonin in plants, which is called also phytomelatonin [25], was detected in 1995 by various research groups [22,[26][27][28]. The MT molecule plays crucial roles in an extensive variety of physiological processes, e.g., germination, root and shoot growth, photosynthesis, stomatal closure, osmoregulation, secondary metabolism, leaf senescence, circadian cycle regulation, flowering, and fruit setting, and in the protection against biotic and abiotic factors [29][30][31][32][33]. The identification in the model plant Arabidopsis thaliana of the first plant melatonin receptor, named PHYTOMELATONIN RECEPTOR 1 (AtPMTR1) [34], unlocked the door to be considered a new plant hormone [29].…”

Current research and future directions of melatonin's role in seed germination

“…In 2018, the first phytomelatonin receptor (PMTR1) has been found in Arabidopsis thaliana (Wei et al 2018 ). Further studies have found that PMTR1 is required for perceiving melatonin signaling in the regulation of stomatal closure and stomatal immunity, seed germination and seedling growth, flowering, resistance to drought, salt and high light stresses, and leaf senescence (Khan et al 2023 ; Li et al 2020a ; Wei et al 2018 ; Yang et al 2021a ; Yin et al 2022 ).…”