Abstract
Melatonin is a well-known bioactive molecule with an array of health-promoting properties. Here, we detected the physiological function of melatonin in transgenic switchgrass overexpressing the homologous sheep arylalkylamine N-acetyltransferase and hydroxyindole O-methyltransferase genes, which catalyze the last two steps of melatonin synthesis. Compared to the wild-type (WT) and transgenic control (EV, expressing the empty vector only) plants, the transgenic switchgrass showed higher melatonin levels. Melatonin was detected in almost all switchgrass tissues, and relatively higher levels were detected in the roots and stems. Besides, melatonin showed diurnal or circadian rhythms in switchgrass similar to that in other species. Furthermore, we also found that melatonin positively affected switchgrass growth, flowering and salt tolerance. The genes related to flowering (APL3, SL1, FT1, FLP3, MADS6 and MADS15) and salt stress resistance (PvNHX1) in transgenic switchgrass exhibited a different expression profiles when compared to the control plants. Our study provided valuable findings that melatonin functions as a promoter in the regulation of switchgrass growth, flowering and salt tolerance.
Highlights
Melatonin (N-acetyl-5-methoxytryptamine), a well-known indole molecule, has a low molecular weight and simple structure
One to five copies of oAANAT and oHIOMT genes were stably integrated into these transgenic lines
Results from both the polymerase chain reaction (PCR) and Southern blot analysis confirmed that the oAANAT and oHIOMT genes were incorporated into the switchgrass genome
Summary
Melatonin (N-acetyl-5-methoxytryptamine), a well-known indole molecule, has a low molecular weight and simple structure. Melatonin biosynthesis begins with tryptophan and consists of four-step reactions in plants, but at least six enzymes are involved in this pathway with multiple (at least four) routes[11,12,13]. Among these enzymes, tryptophan decarboxylase (TDC), tryptamine 5-hydroxylase (T5H), serotonin N-acetyltransferase (SNAT), N-acetylserotonin methyltransferase (ASMT), and caffeic acid O-methyltransferase (COMT), have been characterized at the biochemical and molecular levels, whereas the tryptophan hydroxylase (TPH) has not been studied. Introduction of growth and stress-tolerance genes through tissue culture and genetic transformation methods are expected to be more efficient in generating novel switchgrass plants with improved stress tolerance
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