Abstract
Melatonin serves important functions in the promotion of growth and anti-stress regulation by efficient radical scavenging and regulation of antioxidant enzyme activity in various plants. To investigate its regulatory roles and metabolism pathways, the transcriptomic profile of overexpressing the ovine arylalkylamine N-acetyltransferase (oAANAT) gene, encoding the penultimate enzyme in melatonin biosynthesis, was compared with empty vector control using RNA-seq in switchgrass, a model plant of cellulosic ethanol conversion. The 85.22 million high quality reads that were assembled into 135,684 unigenes were generated by Illumina sequencing for transgenic oAANAT switchgrass with an average sequence length of 716 bp. A total of 946 differentially expression genes in transgenic line comparing to control switchgrass, including 737 up-regulated and 209 down-regulated genes, were mainly enriched with two main functional patterns of melatonin identifying by gene ontology analysis: the growth regulator and stress tolerance. Furthermore, KEGG maps indicated that the biosynthetic pathways of secondary metabolite (phenylpropanoids, flavonoids, steroids, stilbenoid, diarylheptanoid, and gingerol) and signaling pathways (MAPK signaling pathway, estrogen signaling pathway) were involved in melatonin metabolism. This study substantially expands the transcriptome information for switchgrass and provides valuable clues for identifying candidate genes involved in melatonin biosynthesis and elucidating the mechanism of melatonin metabolism.
Highlights
Since melatonin (N-acetyl-5-methoxytryptamine) was first discovered in plant in Dubbels et al (1995) and Hattori et al (1995), varying concentrations of melatonin have been found in many other plant species (Murch et al, 1997; Manchester et al, 2000; Simopoulos et al, 2005)
A growing body of molecular and gene expression research regarding melatonin has been documented on model plants (Kang et al, 2010; Park et al, 2012; Byeon et al, 2013b; Weeda et al, 2014), the expression profiling of genes on melatonin biosynthesis and metabolism in forage grass has not yet been investigated, which was potentially valuable for the molecular breeding of the switchgrass as an superior bioethanol grass
Through the classic view supports the last HIOMT/acetylserotonin O-methyltransferase (ASMT) enzyme is rate-limiting during the biosynthesis of melatonin, the promotional roles of AANAT/serotonin N-acetyltransferase (SNAT) were reported in other species, e.g., the ovine arylalkylamine N-acetyltransferase (oAANAT) transgenic ‘micro-tom’ tomato have higher melatonin levels than control (Wang et al, 2014)
Summary
Since melatonin (N-acetyl-5-methoxytryptamine) was first discovered in plant in Dubbels et al (1995) and Hattori et al (1995), varying concentrations of melatonin have been found in many other plant species (Murch et al, 1997; Manchester et al, 2000; Simopoulos et al, 2005). The fundamental issues of melatonin biosynthetic pathways and physiological functions still need to be deciphered to utilize in plants (Tan et al, 2003, 2012; Arnao and Hernández-Ruiz, 2009; Arnao, 2014; Wei et al, 2016) Both exogenous melatonin treatments (Kolár et al, 2003; Arnao and Hernández-Ruiz, 2007; Sarropoulou et al, 2012; Zhang et al, 2013) and melatonin-rich transgenic plants (Kang et al, 2010; Park et al, 2012; Byeon and Back, 2014; Wang et al, 2014) have been carried on in order to determine its potential functional roles. Overexpression of AANAT gene can promote the ability of biosynthesis of melatonin, and significantly improve the melatonin content in plants (Kang et al, 2010; Wang et al, 2014; Zhang et al, 2014)
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