Abstract
Melatonin can increase plant resistance to stress, and exogenous melatonin has been reported to promote stress resistance in plants. In this study, a melatonin biosynthesis-related SlCOMT1 gene was cloned from tomato (Solanum lycopersicum Mill. cv. Ailsa Craig), which is highly expressed in fruits compared with other organs. The protein was found to locate in the cytoplasm. Melatonin content in SlCOMT1 overexpression transgenic tomato plants was significantly higher than that in wild-type plants. Under 800 mM NaCl stress, the transcript level of SlCOMT1 in tomato leaf was positively related to the melatonin contents. Furthermore, compared with that in wild-type plants, levels of superoxide and hydrogen peroxide were lower while the content of proline was higher in SlCOMT1 transgenic tomatoes. Therefore, SlCOMT1 was closely associated with melatonin biosynthesis confers the significant salt tolerance, providing a clue to cope with the growing global problem of salination in agricultural production.
Highlights
Melatonin (N-acetyl-5-methoxytryptamine) is known as the pineal hormone, because it was first detected in the pineal gland of cattle by Lerner and colleagues in 1958 [1]
Five COMT homologous genes were identified in the tomato genome, and the melatonin synthesis-related gene SlCOMT1 was isolated based on homology comparison using
SlCOMT1 protein was localized in the cytoplasm, suggesting that it might catalyze serotonin into 5-methoxytryptamine in the cytoplasm
Summary
Melatonin (N-acetyl-5-methoxytryptamine) is known as the pineal hormone, because it was first detected in the pineal gland of cattle by Lerner and colleagues in 1958 [1]. In addition to its physiochemical functions in mammals, melatonin plays important roles in plant physiology [7]. Afterwards, serotonin is converted into N-acetylserotonin in the chloroplast and 5-methoxytryptamine in the cytoplasm by SNAT and ASMT, through acetylation and methylation, respectively. In Arabidopsis, serotonin can be converted to 5-methoxytryptamine by COMT methylation in the third step of melatonin synthesis, and catalyzed by SNAT to melatonin [27]. Some plants, including dicots, lack ASMT homologs, suggesting that COMT plays an important role in the last step of melatonin synthesis [26,27]. COMT gene improves melatonin production and positively contributes to strengthen both biotic and abiotic stress resistance in plants [29,30]. Several investigators have studied the effects of exogenous melatonin on tomato plants exposed to abiotic stress. The relationship between melatonin production and salt resistance of transgenic tomato plants was investigated
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