Arabidopsis Transcriptome Analysis Reveals Key Roles of Melatonin in Plant Defense Systems

Abstract

Melatonin is a ubiquitous molecule and exists across kingdoms including plant species. Studies on melatonin in plants have mainly focused on its physiological influence on growth and development, and on its biosynthesis. Much less attention has been drawn to its affect on genome-wide gene expression. To comprehensively investigate the role(s) of melatonin at the genomics level, we utilized mRNA-seq technology to analyze Arabidopsis plants subjected to a 16-hour 100 pM (low) and 1 mM (high) melatonin treatment. The expression profiles were analyzed to identify differentially expressed genes. 100 pM melatonin treatment significantly affected the expression of only 81 genes with 51 down-regulated and 30 up-regulated. However, 1 mM melatonin significantly altered 1308 genes with 566 up-regulated and 742 down-regulated. Not all genes altered by low melatonin were affected by high melatonin, indicating different roles of melatonin in regulation of plant growth and development under low and high concentrations. Furthermore, a large number of genes altered by melatonin were involved in plant stress defense. Transcript levels for many stress receptors, kinases, and stress-associated calcium signals were up-regulated. The majority of transcription factors identified were also involved in plant stress defense. Additionally, most identified genes in ABA, ET, SA and JA pathways were up-regulated, while genes pertaining to auxin responses and signaling, peroxidases, and those associated with cell wall synthesis and modifications were mostly down-regulated. Our results indicate critical roles of melatonin in plant defense against various environmental stresses, and provide a framework for functional analysis of genes in melatonin-mediated signaling pathways.

Regulatory roles of serotonin and melatonin in abiotic stress tolerance in plants

“…14,20 Further classification has shown major genes to be expressed in the cytoplasm, nucleus and plasma membrane. Different set of genes are affected by exogenous melatonin.…”

“…Transcriptomic analysis in Arabidopsis has shown 183 genes to be associated with melatonin-induced changes in hormonal signaling. 20 Auxin responsive genes exhibit both up and down regulation in response to melatonin. Auxin transport and homeostasis are, thus, under the precise regulation by melatonin though it does not seem to affect the expression of auxin biosynthetic genes.…”

“…Auxin transport and homeostasis are, thus, under the precise regulation by melatonin though it does not seem to affect the expression of auxin biosynthetic genes. 20 Although abiotic stressinduced lowering of auxin levels may affect plant growth, serotonin and melatonin partially ameliorate stressinduced inhibitory effects. Ethylene and abscisic acid biosynthetic pathway genes also seem to be regulated by melatonin availability in Arabidopsis.…”

“…Upregulation of 2 ACC synthase genes in response to melatonin suggests its role in the induction of ethylene biosynthesis. 20 Melatonin-induced upregulation of abscisic acid, salicylic acid, jasmonic acid and ethylene biosynthetic pathway genes modulates several hormonal responses, thereby affecting plant defense processes. These hormone biosynthetic genes modulate their expression in response to abiotic and biotic stress even in the absence of melatonin.…”

“…These hormone biosynthetic genes modulate their expression in response to abiotic and biotic stress even in the absence of melatonin. 20 Exogenous melatonin treatment in cucumber seedlings induced down regulation of ABA biosynthetic genes whereas GA biosynthetic genes were upregulated to provide necessary tolerance to NaCl stress. 79 Thus, a hormonal crosstalk during abiotic stress appears to be regulated by melatonin.…”