Molecular Mechanism Of Melatonin And Its Homologs,5-Methoxyindole Induce The Plant Response As Well As The Two Compounds Adverse Effect On Phytopathogenic Microorganisms

Melatonin（N-acetyl-5-Methoxytryptamine）,a naturally-occurring,small molecule,serves as an important secondary messenger in plant immunity.It is not known,however,if melatonin homologs,such as 5-Methoxyindole,that are easy and more cost-effective to synthesize,can stimulate the plant immune system in the same manner as melatonin;widely inhibit the plant pathology;in addition,the mechanism of the two compounds antagonistic activity in the microorganisms.In this study,the antagonistic activity of the melatonin and its homologs and the plant pathways induced by the two compounds were investigated.The main research results are as follows:In the present study,we assessed the biological activity of the melatonin homologs,5-Methoxytryptamin and 5-Methoxyindole.The results indicated that these homologs,such as 5-Methoxyindole which represent the functional backbone of melatonin,exhibited an effect on the induction of plant immunity in manner similar to melatonin.Melatonin,5-Methoxytryptamine,and 5-Methoxyindole all induced disease resistance against Phytophthora nicotianae in N.benthamiana plants.The application of all three compounds also induced stomatal closure and the production of reactive oxygen species.Reverse transcription-quantitative PCR（RT-q PCR）analysis indicated that the expression of genes involved in H₂O₂,NO production,and SA biosynthesis was significantly up-regulated by all three compounds.Bioinformatic analysis and a molecular docking study were used to identify four putative melatonin receptors in N.benthamiana.Further experimentation revealed that silencing of the putative melatonin receptors trP47363 and trP13076 in N.benthamiana compromised the induction of stomatal closure,PR-1a expression and SA accumulation by all three compounds.Collectively,our data indicate that the induction of defense responses in N.benthamiana by melatonin,5-Methoxytryptamine,and5-Methoxyindole involves the putative melatonin receptors trP47363 and trP13076.At present,a large number of studies identify that melatonin not only has broad-spectrum physiological activity in humans and animals,but also directly induces the immune response of plants.However,the effect of the melatonin and its homolog in the large number of the plant pathology is still litter to know.In this study,it was found that different bacterial pathology（Pantoea ananatis DZ-12,Xanthomonas oryzae pv.oryzicola RS105（Xoc）,Xanthomonas oryzae pv.Oryzicola RS105（Xoc））and the fungu pathology（Fusarium graminearum PH-1,Phytophthora parasitica var.nicotianae）,were treated directly with melatonin and its chemical structure homolog（5-Methoxyindole）.The results show that melatonin and its homology（5-Methoxyindole）not only inhibit the growth of different pathogenic bacteria,but also show the efficient anti-fungal activity to different fungu pathology.In conclution,the results directly show that melatonin and its homolog have a broad-spectrum inhibitory effect on pathogenic microorganisms,which have very important prevention and control potential in the future agriculture.In the present study,5-Methoxyindole,the basic functional homolog of the melatonin,is also involved in the antagonistic interaction with the fungus F.graminearum.After measure the antagonistic interaction of the Melatonin and its homologys with the F.graminearum,our results showed both of the melatonin and 5-Methoxyindole had strong activity against F.graminearum through inbibit the fungus growth,formation and germination of F.graminearum conidia.In addition,melatonin and 5-Methoxyindole could also induce the malformation,the accumulation of reactive oxygen species and caused cell death in F.graminearum hyphae and conidia.F.graminearum secondary metabolism also responded to melatonin and 5-Methoxyindole challenge by increasing the production of deoxynivalenol.In response to melatonin and 5-Methoxyindole,F.graminearum genes involved in scavenging reactive oxygen species were down-regulated,whereas genes involved in the synthesis of deoxynivalenol were up-regulated.In concution,all the findings show the antifungal action of melatonin and 5-Methoxyindole in F.graminearum.With the works of the nano-biochar,nano-biochar can not induce the defense response in N.benthamiana,but also absorbed by plants as the nutrient.However,there is little working in the molecular mechanism of nano-induced plant disease resistance,then the study of nanomaterials has important potential role in the future agricultural applications.In this study,all the nano-biochars induced disease resistance against Phytophthora nicotianae in N.benthamiana plants,and also induced the accumulation of plant H₂O₂ and the ROS-related genes expression.Through the detection of different disease resistance signals（SA,ET,JA）pathways in plants,all the nano-biochar induced plant disease resistance.This study directly proves the nano-biochar can not only induce the disease resistance in plant,but also induced the increase of plant biomass by melatonin homolog（5-Meyhoxyindole）.