Melatonin: Current Status and Future Perspectives in Plant Science

Abstract

Melatonin (N-acetyl-5-methoxytryptamine) is a ubiquitous molecule with pleiotropic actions in different organisms. It performs many important functions in human, animals, and plants; these range from regulating circadian rhythms in animals to controlling senescence in plants. In this review, we summarize the available information regarding the presence of melatonin in different plant species, along with highlighting its biosynthesis and mechanisms of action. We also collected the available information on the effects of melatonin application on commercially important crops to improve their growth and development. Additionally, we have identified many new aspects where melatonin may have possible roles in plants, for example, its function in improving the storage life and quality of fruits and vegetables, its role in vascular reconnection during the grafting process and nutrient uptake from roots by modifying root architecture. Another potentially important aspect is the production of melatonin-rich food crops (cereals, fruits, and vegetables) through combination of conventional and modern breeding approaches, to increase plant resistance against biotic and abiotic stress, leading to improved crop yields, and the nutraceutical value of produce to solve food security issues.

Overexpression of rice serotonin N‐acetyltransferase 1 in transgenic rice plants confers resistance to cadmium and senescence and increases grain yield

“…This growth promotion phenotype was evident both in 7‐day‐old seedling grown in MS medium and in 45‐day‐old rice plants grown in the field . Observations in ovine SNAT transgenic plants confirmed the growth‐promoting roles of melatonin, which had long been observed in several plant species in response to exogenous melatonin treatment . However, the current OsSNAT1 transgenic rice plants lacked such seedling growth promotion effects both in vitro and in vivo in the field (Figure and ) although OsSNAT1 transgenic rice plants produced melatonin at levels comparable to those seen in ovine SNAT transgenic rice plants.…”

“…Since the first discovery of melatonin in plants in 1995, many pharmacological studies have been performed to investigate its functional and physiological significance . Large numbers of experiments involving exogenous application of melatonin to a series of plant species indicated that melatonin acts as a biostimulator in plants by enhancing a myriad of defense responses against abiotic stresses, including oxidative stress, high temperature, cold, senescence, drought, and salt, as well as biotic stress such as pathogen attacks .…”

“…For example, transgenic tobacco plants overexpressing either human arylalkylamine N ‐acetyltransferase ( AANAT or alias SNAT ) or human hydroxyindole O ‐methyltransferase ( HIOMT ) exhibited increased melatonin levels and enhanced antioxidative activities . Thereafter, an array of transgenic plants mainly overexpressing AANAT and HIOMT from animals were generated to uncover new functions or confirm previous functions detected with exogenous melatonin treatment . For example, transgenic rice plants overexpressing animal AANAT showed resistance to cold and oxidative stresses along with delayed flowering and a severe yield penalty .…”

Melatonin production in Escherichia coli by dual expression of serotonin N-acetyltransferase and caffeic acid O-methyltransferase

“…Several highly relevant differences in the melatonin biosynthetic genes between animals and plants were identified through comparisons with the melatonin synthetic capacity in the heterologous E. coli system. When the plant SNAT gene was first cloned from rice (Kang et al 2013), the purified recombinant SNAT protein had fivefold lower enzyme activity than that of animals, even though the levels of melatonin production are higher in plants than in animals (Voisin et al 1984;Nawaz et al 2016). Thus, clear-cut evidence of a role for a cloned plant SNAT gene in the direct synthesis of melatonin in vivo would be invaluable for heterologous systems such as E. coli.…”

Endophytic Bacterium Pseudomonas fluorescens RG11 May Transform Tryptophan to Melatonin and Promote Endogenous Melatonin Levels in the Roots of Four Grape Cultivars

“…Exogenous melatonin can act as a phytoregulator of seed germination (Zhang et al, 2013, 2014), flowering (Kolář et al, 2003), fruit ripening, anthocyanin accumulation (Sun et al, 2016), root system architecture (Pelagio-Flores et al, 2012), chlorophyll preservation, and leaf senescence (Zhang et al, 2016). It is also a powerful antioxidant that directly decreases the levels of ROS or indirectly modulates antioxidant enzyme activities (Posmyk et al, 2008, 2009; Arnao and Hernández-Ruiz, 2009; Nawaz et al, 2016). Abiotic stressors can elevate the levels of endogenous melatonin in plants (Arnao and Hernández-Ruiz, 2013a,b, 2016; Shi et al, 2015), so stress-induced ROS may trigger melatonin accumulation (Arnao and Hernández-Ruiz, 2015).…”