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Authors: Andrzej Bajguz and Alicja Piotrowska-Niczyporuk.
Metabolites (2023)
Abstract: "Phytohormones exhibit a wide range of chemical structures, though they primarily originate from three key metabolic precursors: amino acids, isoprenoids, and lipids. Specific amino acids, such as tryptophan, methionine, phenylalanine, and arginine, contribute to the production of various phytohormones, including auxins, melatonin, ethylene, salicylic acid, and polyamines. Isoprenoids are the foundation of five phytohormone categories: cytokinins, brassinosteroids, gibberellins, abscisic acid, and strigolactones. Furthermore, lipids, i.e., α-linolenic acid, function as a precursor for jasmonic acid. The biosynthesis routes of these different plant hormones are intricately complex. Understanding of these processes can greatly enhance our knowledge of how these hormones regulate plant growth, development, and physiology. This review focuses on detailing the biosynthetic pathways of phytohormones."
Authors: Antía Verde, Jesús M. Míguez and Mercedes Gallardo.
Postharvest Biology and Technology (2022)
Highlights • Melatonin promotes apple colour and flavor during postharvest, extending firmness. • Melatonin increases ethylene production and advances the climacteric burst. • ACC treatment produces similar effects as melatonin on apple ripening parameters. • Ethylene synthesis is a target for melatonin effects on postharvest apple ripening. • Melatonin up-regulates the expression of MdACS1 and MdACO1 genes in apple skin.
Abstract: "Melatonin has been implicated in the regulation of ripening in several types of climacteric fruits, but its role in apple is poorly understood. In this study, the effectiveness of melatonin in influencing postharvest ripening in apples and interacting with ethylene biosynthesis process was investigated. Apples of four local cultivars (Golden, Reineta, Blanquina and Rabiosa) were harvest at an immature green stage and immersed for 120 min in a solution with water (control), melatonin 50 µM, ACC 1 mM, and melatonin 50 µM + ACC 1 mM. The evolution of apple quality parameters and ethylene production was assessed in all cultivars for 35 days after treatment. In addition, Golden apple was used to examine the transcript abundance of ethylene biosynthesis enzymes genes in the skin and flesh. Exogenous melatonin improved apple quality during postharvest ripening and stimulated ethylene production in all cultivars studied, advancing the timing of the climacteric burst. Melatonin-induced changes in ethylene production correlated well with changes in fruit quality and were in part similar to those induced by the ethylene precursor ACC, so ethylene appears to be a target of melatonin. In Golden apple, melatonin stimulated the expression of MdACS1 and MdACO1 genes, which showed a climacteric profile similar to that of ethylene. The transcriptional effects of exogenous melatonin on ethylene-related genes was also more notable in the skin than in the flesh, suggesting an initiating role of the former in the biosynthesis of the phytohormone. Taken together, the results point to the fact that exogenous melatonin may be useful in improving apple quality during postharvest ripening by promoting colour and flavour change and extending fruit firmness. The effect of melatonin appears to be mediated in part by up-regulation of the transcriptional activity of the MdACS1 and MdACO1 genes during the climacteric peak, thus contributing to an increase in ethylene availability."
Authors: Chuang Liu, Hui Kang, Yafang Wang, Yuxin Yao, Zhen Gao and Yuanpeng Du.
Frontiers in Pant Science (2021)
Abstract: "Ozone (O3) stress severely affects the normal growth of grape (Vitis vinifera L.) leaves. Melatonin (MT) plays a significant role in plant response to various abiotic stresses, but its role in O3 stress and related mechanisms are poorly understood. In order to understand the mechanism of MT in alleviate O3 stress in grape leaves, we perform a transcriptome analyses of grapes leaves under O3 stress with or without MT treatment. Transcriptome analysis showed that the processes of ethylene biosynthesis and signaling were clearly changed in “Cabernet Sauvignon” grapes under O3 and MT treatment. O3 stress induced the expression of genes related to ethylene biosynthesis and signal transduction, while MT treatment significantly inhibited the ethylene response mediated by O3 stress. Further experiments showed that both MT and aminoethoxyvinylglycine (AVG, an inhibitor of ethylene biosynthesis) enhanced the photosynthetic and antioxidant capacities of grape leaves under O3 stress, while ethephon inhibited those capacities. The combined treatment effect of MT and ethylene inhibitor was similar to that of MT alone. Exogenous MT reduced ethylene production in grape leaves under O3 stress, while ethephon and ethylene inhibitors had little effect on the MT content of grape leaves after O3 stress. However, overexpression of VvACO2 (1-aminocyclopropane-1-carboxylate oxidase2) in grape leaves endogenously induced ethylene accumulation and aggravated O3 stress. Overexpression of the MT synthesis gene VvASMT1 (acetylserotonin methyltransferase1) in tobacco (Nicotiana tabacum L.) alleviated O3 stress and reduced ethylene biosynthesis after O3 stress. In summary, MT can alleviate O3 stress in grape leaves by inhibiting ethylene biosynthesis."
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Authors: Muhammad Saad Shoaib Khan, Sulaiman Ahmed, Aziz ul Ikram, Fakhir Hannan, Muhammad Umair Yasin, Jin Wang, Biying Zhao, Faisal Islam and Jian Chen.
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."
Authors: Shuangshuang Shan, Zhiqiang Wang, Huili Pu, Wenhui Duan, Hongmiao Song, Jiangkuo Li, Zhengke Zhang and Xiangbin Xu.
Scientia Horticulturae (2021)
Highlights: • Melatonin significantly promoted ripening of postharvest tomato fruit. • Melatonin changed the DNA methylation level of ethylene signaling genes. • Melatonin treatment induced the expression level of ethylene signaling genes. • The dynamic changes of DNA methylation were involved in fruit ripening.
Abstract: "Melatonin (MT) as an evolutionarily highly conserved molecule plays an exceptional role in plants. In the present study, the regulation mechanism of the DNA methylation of CpG islands of ethylene signaling genes induced by MT on postharvest ripening of tomato fruit was studied. The ripening of tomato fruit was significantly promoted by the 0.5 mM MT treatment, as revealed by the appearance color, the lycopene, total soluble solids and vitamin C content of the fruit. In the MT treated fruit, the DNA methylation levels of CpG island of SlACS10 and SlERF-A1 were decreased, and the DNA methylation level of CpG island of SlCTR1 was increased. In addition, MT treatment increased the expression level of SlACS10, SlEIN3, SlERF-A1 and SlERT10, inhibited the expression level of SlCTR1, and by which the ethylene signaling might be activated and the ripening was promoted. The effect of MT on the DNA methylation of CpG islands of genes involved in ethylene signaling may contribute to the ripening of tomato fruit. The present study provided valuable information for understanding the essential role of DNA methylation in the postharvest ripening of tomato fruit."
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