Melatonin and Its Homologs Induce Immune Responses via Receptors trP47363-trP13076 in Nicotiana benthamiana

Abstract

Melatonin (N-acetyl-5-methoxytryptamine), a naturally occurring small molecule, can protect plants against abiotic stress after exogenous treatmenting with it. It is not known if melatonin homologs, such as 5-methoxytryptamine and 5-methoxyindole, that are easy and more cost-effective to synthesize can stimulate the plant immune system in the same manner as melatonin. In the present study, we assessed the biological activity of the melatonin homologs, 5-methoxytryptamin and 5-methoxyindole. The results showed that melatonin and its homologs all induced disease resistance against Phytophthora nicotianae in Nicotiana benthamiana plants. The application of all three compounds also induced stomatal closure and the production of reactive oxygen species. Gene expression analysis indicated that the expression of genes involved in hydrogen peroxide (H2O2), nitric oxide (NO) production, and salicylic acid (SA) biosynthesis was significantly upregulated by all three compounds. Four homologs of the melatonin receptors were identified by blasting search with the phytomelatonin receptor in Arabidopsis. Molecular docking studies were also used to identify four putative melatonin receptors in N. benthamiana. Further experimentation revealed that silencing of the melatonin receptors trP47363 and trP13076 in N. benthamiana compromised the induction of stomatal closure, PR-1a gene 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, and 5-methoxyindole involves the melatonin receptors trP47363 and trP13076.

Toxicity of Bacillus thuringiensis Strains Derived from the Novel Crystal Protein Cry31Aa with High Nematicidal Activity against Rice Parasitic Nematode Aphelenchoides besseyi

“…Bt can also directly promote plant growth by synthesizing phosphate lysing enzymes [ 60 ], siderophores [ 61 ], and plant hormones [ 62 , 63 ]. When analyzing the growth-promoting effects of GBAC46 and NMTD81 strains in rice, it was found that the selected strains significantly promoted rice physiological parameters such as root and shoot length [ 10 , 28 ].…”

Crosstalk between Melatonin and Reactive Oxygen Species in Plant Abiotic Stress Responses: An Update

“…Several studies take the important stance that the transmembrane receptor of melatonin (PMTR1/CAND2) is found in Arabidopsis , tobacco, alfalfa, and maize [ 116 , 117 , 118 , 119 ]. It is also located in the plasma membrane, and can interact with G-protein α subunits, thereby activating RBOHs to promote stomatal closure in Arabidopsis ( Figure 2 ) [ 116 , 119 ].…”

5-Methoxyindole, a Chemical Homolog of Melatonin, Adversely Affects the Phytopathogenic Fungus Fusarium graminearum

“…The impacts of several melatonin homologs on disease resistance against P. nicotianae and stomatal closure were investigated in N. benthamiana. The results showed that the melatonin homolog 5-methoxyindole could induce plant immunity by inducing stomatal closure, similar to melatonin in N. benthamiana [29]. Then, to identify the fungicidal activity of various concentrations of melatonin and its homolog 5-methoxyindole against F. graminearum, water was used as a negative control and melatonin was used as a positive control.…”

“…For example, phytomelatonin regulation of stomatal closure is dependent on its receptor CAND2/PMTR1-mediated H 2 O 2 and the Ca 2+ signaling transduction cascade after treatment with 10 µM melatonin [26], and 10 µM melatonin is responsible for rice resistance to rice stripe virus infection through a nitric oxide-dependent pathway [27]. Melatonin application reduces fluoride uptake and toxicity in rice seedlings by altering abscisic acid (ABA), gibberellin (GA), auxin, and antioxidant homeostasis after treatment with 20 and 100 µM melatonin, and its homologs induce immune responses via receptors trP47363-trP13076 in Nicotiana benthamiana [28,29].…”