BACKGROUND Melatonin (N-acetyl-5-methoxytryptamine) in plants, regulates shoot and root growth and alleviates environmental stresses. Melatonin and the phyto-hormone auxin are tryptophan-derived compounds. However, it largely remains controversial as to whether melatonin and auxin act through similar or overlapping signalling and regulatory pathways. RESULTS Here, we have used a promoter-activation study to demonstrate that, unlike auxin (1-naphthalene acetic acid, NAA), melatonin neither induces Direct repeat 5 DR5 expression in Arabidopsis thaliana roots under normal growth conditions nor suppresses the induction of Alternative oxidase 1a AOX1a in leaves upon Antimycin A treatment, both of which are the hallmarks of auxin action. Additionally, comparative global transcriptome analysis conducted on Arabidopsis treated with melatonin or NAA revealed differences in the number and types of differentially expressed genes. Auxin (4.5 μM) altered the expression of a diverse and large number of genes whereas melatonin at 5 μM had no significant effect but melatonin at 100 μM had a modest effect on transcriptome compared to solvent-treated control. Interestingly, the prominent category of genes differentially expressed upon exposure to melatonin trended towards biotic stress defence pathways while downregulation of key genes related to photosynthesis was observed. CONCLUSION Together these findings indicate that though they are both indolic compounds, melatonin and auxin act through different pathways to alter gene expression in Arabidopsis thaliana. Furthermore, it appears that effects of melatonin enable Arabidopsis thaliana to prioritize biotic stress defence signalling rather than growth. These findings clear the current confusion in the literature regarding the relationship of melatonin and auxin and also have greater implications of utilizing melatonin for improved plant protection.

中文翻译：

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直接比较拟南芥基因表达揭示褪黑素与生长素的不同反应。

背景技术植物中的褪黑素（N-乙酰基-5-甲氧基色胺）调节芽和根的生长并减轻环境压力。褪黑激素和植物激素生长素是色氨酸衍生的化合物。然而，关于褪黑激素和生长素是否通过相似或重叠的信号传导和调节途径起作用，仍然存在很大争议。结果在这里，我们已经使用启动子激活研究来证明，与生长素（1-萘乙酸，NAA）不同，褪黑素在正常生长条件下既不会诱导拟南芥根中直接重复5 DR5表达，也不会抑制其他氧化酶的诱导。抗霉素A处理后叶片中的1a AOX1a都是生长素作用的标志。此外，在用褪黑激素或NAA处理的拟南芥上进行的比较性全球转录组分析表明，差异表达基因的数量和类型存在差异。生长素（4.5μM）改变了多种基因的表达，而与溶剂处理的对照相比，5μM的褪黑素无明显作用，但100μM的褪黑素对转录组影响中等。有趣的是，在暴露于褪黑素时差异表达的基因的显着类别趋向于生物胁迫防御途径，同时观察到与光合作用相关的关键基因的下调。结论这些发现共同表明，褪黑素和生长素虽然都是吲哚类化合物，但它们通过不同的途径起作用来改变拟南芥中的基因表达。此外，褪黑素的作用似乎使拟南芥能够优先考虑生物胁迫防御信号而不是生长。这些发现清除了目前关于褪黑激素和生长素关系的文献混乱，并且对于利用褪黑激素改善植物保护也具有更大的意义。