Suppression of Melatonin 2-Hydroxylase Increases Melatonin Production Leading to the Enhanced Abiotic Stress Tolerance against Cadmium, Senescence, Salt, and Tunicamycin in Rice Plants

Choi, Geun-Hee; Back, Kyoungwhan

doi:10.3390/biom9100589

Cited by 33 publications

(31 citation statements)

References 61 publications

(99 reference statements)

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“…TDC RNAi, T5H knockout mutant, and COMT RNAi rice plants were described previously [23]. TDC RNAi and COMT RNAi rice plants were generated by Agrobacterium -mediated transformation using the same pTCK303 binary vector described previously [23,69]. T5H mutant rice plants lacking a functional T5H gene were screened from 137 Cs-irradiated Ashahi seeds and obtained from the National Institute of Agrobiological Sciences (NIAS) GeneBank ().…”

Section: Methodsmentioning

confidence: 99%

Melatonin Deficiency Confers Tolerance to Multiple Abiotic Stresses in Rice via Decreased Brassinosteroid Levels

Hwang

Back

2019

IJMS

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Melatonin has long been recognized as a positive signaling molecule and potent antioxidant in plants, which alleviates damage caused by adverse conditions such as salt, cold, and heat stress. In this study, we found a paradoxical role for melatonin in abiotic stress responses. Suppression of the serotonin N-acetyltransferase 2 (snat2) gene encoding the penultimate enzyme in melatonin biosynthesis led to simultaneous decreases in both melatonin and brassinosteroid (BR) levels, causing a semi-dwarf with erect leaf phenotype, typical of BR deficiency. Here, we further characterized snat2 rice in terms of grain morphology and abiotic stress tolerance, to determine whether snat2 rice exhibited characteristics similar to those of BR-deficient rice. As expected, the snat2 rice exhibited tolerance to multiple stress conditions including cadmium, salt, cold, and heat, as evidenced by decreased malondialdehyde (MDA) levels and increased chlorophyll levels, in contrast with SNAT2 overexpression lines, which were less tolerant to stress than wild type plants. In addition, the length and width of grain from snat2 plants were reduced relative to the wild type, which is reminiscent of BR deficiency in rice. Other melatonin-deficient mutant rice lines with suppressed BR synthesis (i.e., comt and t5h) also showed tolerance to salt and heat stress, whereas melatonin-deficient rice seedlings without decreased BR levels (i.e., tdc) failed to exhibit increased stress tolerance, suggesting that stress tolerance was increased not by melatonin deficiency alone, but by a melatonin deficiency-mediated decrease in BR.

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Section: Methodsmentioning

confidence: 99%

Melatonin Deficiency Confers Tolerance to Multiple Abiotic Stresses in Rice via Decreased Brassinosteroid Levels

Hwang

Back

2019

IJMS

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“…This differential flow promotes differential levels of endogenous melatonin‐related metabolites. For example, serotonin content was around 600 ng g −1 fresh weight (FW) in healthy rice leaves, whereas melatonin content was far lower, at about 0.3 ng g −1 FW, and 3‐OHM and 2‐OHM levels were 100 and 40 ng g −1 FW, respectively, in rice leaves (Lee et al ., 2017; Choi and Back, 2019a,b). Differential levels were also observed in rice leaves challenged with cadmium stress and senescence, such that the melatonin content was much lower than that of its precursor, serotonin (Figure 1b).…”

Section: Involvement Of Multiple Genes In Plant Biosynthesis Of Melatmentioning

confidence: 99%

Melatonin metabolism, signaling and possible roles in plants

2020

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Summary Melatonin is a multifunctional biomolecule found in both animals and plants. In this review, the biosynthesis, levels, signaling, and possible roles of melatonin and its metabolites in plants is summarized. Tryptamine 5‐hydroxylase (T5H), which catalyzes the conversion of tryptamine into serotonin, has been proposed as a target to create a melatonin knockout mutant presenting a lesion‐mimic phenotype in rice. With a reduced anabolic capacity for melatonin biosynthesis and an increased catabolic capacity for melatonin metabolism, all plants generally maintain low melatonin levels. Some plants, including Arabidopsis and Nicotiana tabacum (tobacco), do not possess tryptophan decarboxylase (TDC), the first committed step enzyme required for melatonin biosynthesis. Major melatonin metabolites include cyclic 3‐hydroxymelatonin (3‐OHM) and 2‐hydroxymelatonin (2‐OHM). Other melatonin metabolites such as N1‐acetyl‐N2‐formyl‐5‐methoxykynuramine (AFMK), N‐acetyl‐5‐methoxykynuramine (AMK) and 5‐methoxytryptamine (5‐MT) are also produced when melatonin is applied to Oryza sativa (rice). The signaling pathways of melatonin and its metabolites act via the mitogen‐activated protein kinase (MAPK) cascade, possibly with Cand2 acting as a melatonin receptor, although the integrity of Cand2 remains controversial. Melatonin mediates many important functions in growth stimulation and stress tolerance through its potent antioxidant activity and function in activating the MAPK cascade. The concentration distribution of melatonin metabolites appears to be species specific because corresponding enzymes such as M2H, M3H, catalases, indoleamine 2,3‐dioxygenase (IDO) and N‐acetylserotonin deacetylase (ASDAC) are differentially expressed among plant species and even among different tissues within species. Differential levels of melatonin and its metabolites can lead to differential physiological effects among plants when melatonin is either applied exogenously or overproduced through ectopic overexpression.

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“…For example, melatonin treatment enhances plant tolerance against many stresses, including salt [6,7], drought [8,9], viruses [10], pathogens [11,12], waterlogging [13], and senescence [14], among others [15][16][17]. Melatonin is also involved in plant development processes such as growth [18,19], seed viability [20], flowering [21,22], endoplasmic reticulum (ER) quality control [23,24], secondary metabolite synthesis [25], and others [26]. The pleiotropic effects of melatonin are due to the combined effects of its antioxidant activity and signaling or hormonal activity [5], although its metabolites, such as 2-hydroxymelatonin and cyclic 3-hydroxymelatonin, are also involved in physiological activity such as tiller growth [27,28].…”

Section: Introductionmentioning

confidence: 99%

Effects of Light Quality and Phytochrome Form on Melatonin Biosynthesis in Rice

2020

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Light is an important factor influencing melatonin synthesis in response to cadmium treatment in rice. However, the effects of light quality on, and the involvement of phytochrome light receptors in, melatonin production have not been explored. In this study, we used light-emitting diodes (LEDs) to investigate the effect of light wavelength on melatonin synthesis, and the role of phytochromes in light-dependent melatonin induction in rice. Upon cadmium treatment, peak melatonin production was observed under combined red and blue (R + B) light, followed by red (R) and blue light (B). However, both far-red (FR) LED light and dark treatment (D) failed to induce melatonin production. Similarly, rice seedlings grown under the R + B treatment showed the highest melatonin synthesis, followed by those grown under B and R. These findings were consistent with the results of our cadmium treatment experiment. To further confirm the effects of light quality on melatonin synthesis, we employed rice photoreceptor mutants lacking functional phytochrome genes. Melatonin induction was most inhibited in the phytochrome A mutant (phyA) followed by the phyB mutant under R + B treatment, whereas phyB produced the least amount of melatonin under R treatment. These results indicate that PhyB is an R light receptor. Expression analyses of genes involved in melatonin biosynthesis clearly demonstrated that tryptophan decarboxylase (TDC) played a key role in phytochrome-mediated melatonin induction when rice seedlings were challenged with cadmium.

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Suppression of Melatonin 2-Hydroxylase Increases Melatonin Production Leading to the Enhanced Abiotic Stress Tolerance against Cadmium, Senescence, Salt, and Tunicamycin in Rice Plants

Cited by 33 publications

References 61 publications

Melatonin Deficiency Confers Tolerance to Multiple Abiotic Stresses in Rice via Decreased Brassinosteroid Levels

Melatonin Deficiency Confers Tolerance to Multiple Abiotic Stresses in Rice via Decreased Brassinosteroid Levels

Melatonin metabolism, signaling and possible roles in plants

Effects of Light Quality and Phytochrome Form on Melatonin Biosynthesis in Rice

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