J. Pineal Res. 2015; 58:470–478
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Molecular, Biological, Physiological and Clinical Aspects of Melatonin
Doi:10.1111/jpi.12232
Journal of Pineal Research
Coordinated regulation of melatonin synthesis and degradation genes in rice leaves in response to cadmium treatment Abstract: We investigated the expression patterns of genes involved in melatonin synthesis and degradation in rice leaves upon cadmium (Cd) treatment and the subcellular localization sites of melatonin 2-hydroxylase (M2H) proteins. The Cd-induced synthesis of melatonin coincided with the increased expression of melatonin biosynthetic genes including tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), and N-acetylserotonin methyltransferase (ASMT). However, the expression of serotonin Nacetyltransferase (SNAT), the penultimate gene in melatonin biosynthesis, was downregulated, suggesting that melatonin synthesis was counter-regulated by SNAT. Notably, the induction of melatonin biosynthetic gene expression was coupled with the induction of four M2H genes involved in melatonin degradation, which suggests that genes for melatonin synthesis and degradation are coordinately regulated. The induced M2H gene expression was correlated with enhanced M2H enzyme activity. Three of the M2H proteins were localized to the cytoplasm and one M2H protein was localized to chloroplasts, indicating that melatonin degradation occurs both in the cytoplasm and in chloroplasts. The biological activity of 2-hydroxymelatonin in the induction of the plant defense gene expression was 50% less than that of melatonin, which indicates that 2-hydroxymelatonin may be a metabolite of melatonin. Overall, our data demonstrate that melatonin synthesis occurs in parallel with melatonin degradation in both chloroplasts and cytoplasm, and the resulting melatonin metabolite 2-hydroxymelatonin also acts as a signaling molecule for defense gene induction.
Introduction Melatonin, which is ubiquitous among organisms (including animals and plants) [1–3], has a variety of biological roles. In animals, melatonin has many functions including its prominent role as a regulator of sleep/wake cycles [3, 4] and as a potent antioxidant [5, 6]. It is also contributes to stem cell differentiation [7], anti-osteoporosis [8], antiaging [9], innate immunity [10], anti-inflammation [11], and life span extension [12]. Melatonin also plays many roles in plants including involvement in plant growth and development [13, 14], and in defense against various abiotic and biotic stresses [13–16]. Unlike in animals, however, melatonin does not appear to function in plants as a hormone associated with the day/night cycle [17], although melatonin levels have been shown to increase at night in at least one species [18]. Concurrent with advances in our knowledge regarding the physiological roles of melatonin in plants, rapid progress has been made in identifying the components of the melatonin biosynthetic pathway. The plant melatonin biosynthesis pathway, which begins with tryptophan and proceeds in four steps, as it does in animals, is now well established [3, 19]. The first committed step for melatonin biosynthesis in plants is catalyzed by tryptophan 470
Yeong Byeon*, Hyoung Yool Lee*, Ok Jin Hwang, Hye-Jung Lee, Kyungjin Lee and Kyoungwhan Back Department of Biotechnology, Bioenergy Research Center, College of Agriculture and Life Sciences, Chonnam National University, Gwangju, South Korea
Key words: 2-hydroxymelatonin, 2-oxoglutaratedependent dioxygenases, cadmium, melatonin 2-hydroxygenase, subcellular localization Address reprint requests to Kyoungwhan Back, Department of Biotechnology, Bioenergy Research Center, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, South Korea. E-mail: [email protected] *These authors contributed equally to this work. Received February 20, 2015; Accepted March 13, 2015.
decarboxylase (TDC), which converts tryptophan to tryptamine [19, 20] and is followed by tryptamine 5-hydroxylase (T5H), which converts tryptamine to serotonin [21, 22]. The penultimate and final steps of melatonin synthesis are catalyzed by serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT), respectively, which carry out the sequential conversion of serotonin to N-acetylserotonin and melatonin. Melatonin biosynthesis is divided into two separate metabolic steps: from tryptophan to serotonin and from serotonin to melatonin. Serotonin was shown to accumulate during senescence in rice leaves to levels as high as 1600 lg/g fresh weight (FW) [23], but melatonin levels remained
© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Molecular, Biological, Physiological and Clinical Aspects of Melatonin
Doi:10.1111/jpi.12232
Journal of Pineal Research
Coordinated regulation of melatonin synthesis and degradation genes in rice leaves in response to cadmium treatment Abstract: We investigated the expression patterns of genes involved in melatonin synthesis and degradation in rice leaves upon cadmium (Cd) treatment and the subcellular localization sites of melatonin 2-hydroxylase (M2H) proteins. The Cd-induced synthesis of melatonin coincided with the increased expression of melatonin biosynthetic genes including tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), and N-acetylserotonin methyltransferase (ASMT). However, the expression of serotonin Nacetyltransferase (SNAT), the penultimate gene in melatonin biosynthesis, was downregulated, suggesting that melatonin synthesis was counter-regulated by SNAT. Notably, the induction of melatonin biosynthetic gene expression was coupled with the induction of four M2H genes involved in melatonin degradation, which suggests that genes for melatonin synthesis and degradation are coordinately regulated. The induced M2H gene expression was correlated with enhanced M2H enzyme activity. Three of the M2H proteins were localized to the cytoplasm and one M2H protein was localized to chloroplasts, indicating that melatonin degradation occurs both in the cytoplasm and in chloroplasts. The biological activity of 2-hydroxymelatonin in the induction of the plant defense gene expression was 50% less than that of melatonin, which indicates that 2-hydroxymelatonin may be a metabolite of melatonin. Overall, our data demonstrate that melatonin synthesis occurs in parallel with melatonin degradation in both chloroplasts and cytoplasm, and the resulting melatonin metabolite 2-hydroxymelatonin also acts as a signaling molecule for defense gene induction.
Introduction Melatonin, which is ubiquitous among organisms (including animals and plants) [1–3], has a variety of biological roles. In animals, melatonin has many functions including its prominent role as a regulator of sleep/wake cycles [3, 4] and as a potent antioxidant [5, 6]. It is also contributes to stem cell differentiation [7], anti-osteoporosis [8], antiaging [9], innate immunity [10], anti-inflammation [11], and life span extension [12]. Melatonin also plays many roles in plants including involvement in plant growth and development [13, 14], and in defense against various abiotic and biotic stresses [13–16]. Unlike in animals, however, melatonin does not appear to function in plants as a hormone associated with the day/night cycle [17], although melatonin levels have been shown to increase at night in at least one species [18]. Concurrent with advances in our knowledge regarding the physiological roles of melatonin in plants, rapid progress has been made in identifying the components of the melatonin biosynthetic pathway. The plant melatonin biosynthesis pathway, which begins with tryptophan and proceeds in four steps, as it does in animals, is now well established [3, 19]. The first committed step for melatonin biosynthesis in plants is catalyzed by tryptophan 470
Yeong Byeon*, Hyoung Yool Lee*, Ok Jin Hwang, Hye-Jung Lee, Kyungjin Lee and Kyoungwhan Back Department of Biotechnology, Bioenergy Research Center, College of Agriculture and Life Sciences, Chonnam National University, Gwangju, South Korea
Key words: 2-hydroxymelatonin, 2-oxoglutaratedependent dioxygenases, cadmium, melatonin 2-hydroxygenase, subcellular localization Address reprint requests to Kyoungwhan Back, Department of Biotechnology, Bioenergy Research Center, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, South Korea. E-mail: [email protected] *These authors contributed equally to this work. Received February 20, 2015; Accepted March 13, 2015.
decarboxylase (TDC), which converts tryptophan to tryptamine [19, 20] and is followed by tryptamine 5-hydroxylase (T5H), which converts tryptamine to serotonin [21, 22]. The penultimate and final steps of melatonin synthesis are catalyzed by serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT), respectively, which carry out the sequential conversion of serotonin to N-acetylserotonin and melatonin. Melatonin biosynthesis is divided into two separate metabolic steps: from tryptophan to serotonin and from serotonin to melatonin. Serotonin was shown to accumulate during senescence in rice leaves to levels as high as 1600 lg/g fresh weight (FW) [23], but melatonin levels remained
