Transcriptome Analysis Reveals the Role of Melatonin in Regulating Crosstalk Among Plant Hormones in Arabidopsis thaliana

Melatonin is a classic animal hormone, but is also present in all investigated plant species.  While little is known about the function of melatonin in plants, it is structurally similar to IAA and has been implicated as a growth regulator. This study was conducted as a first step in deducing the genome-wide affect melatonin has in plants.  Illumina RNA-seq was used to generate transcriptome profiles of Arabidopsis seedlings treated with 0 (control), and 1 mM melatonin.  Nearly 600 genes exhibited a change in transcript levels of at least 2-fold in 1 mM melatonin treated seedlings compared to control, and approximately 60 genes are involved in hormone induced responses and another 40 are involved in other signal transduction pathways.  Interestingly, the majority of the auxin-responsive genes were down-regulated by 1mM melatonin, and nearly all of the SA- and ABA-responsive genes were up-regulated in response to 1 mM melatonin.  Real-time RT-PCR was conducted to validate these transcriptome profiles related to hormonal regulation using both low (100 pM) and high (1 mM) melatonin treated Arabidopsis seedlings. The results showed that most of tested genes were up or down regulated by melatonin, in agreement with genome-wide transcriptome profile, at both melatonin concentrations. However, opposite effect was observed for auxin responsive genes, where high concentration of melatonin suppressed gene(s) expressions, but induced at low melatonin concentration.   These results may suggest the importance of melatonin in control of crosstalk among plant hormones and their regulated signaling pathways.