Abstract
Melatonin is an important secondary messenger in plant innate immunity against the bacterial pathogen Pseudomonas syringe pv. tomato (Pst) DC3000 in the salicylic acid (SA)- and nitric oxide (NO)-dependent pathway. However, the metabolic homeostasis in melatonin-mediated innate immunity is unknown. In this study, comparative metabolomic analysis found that the endogenous levels of both soluble sugars (fructose, glucose, melibose, sucrose, maltose, galatose, tagatofuranose and turanose) and glycerol were commonly increased after both melatonin treatment and Pst DC3000 infection in Arabidopsis. Further studies showed that exogenous pre-treatment with fructose, glucose, sucrose, or glycerol increased innate immunity against Pst DC3000 infection in wild type (Col-0) Arabidopsis plants, but largely alleviated their effects on the innate immunity in SA-deficient NahG plants and NO-deficient mutants. This indicated that SA and NO are also essential for sugars and glycerol-mediated disease resistance. Moreover, exogenous fructose, glucose, sucrose and glycerol pre-treatments remarkably increased endogenous NO level, but had no significant effect on the endogenous melatonin level. Taken together, this study highlights the involvement of sugars and glycerol in melatonin-mediated innate immunity against bacterial pathogen in SA and NO-dependent pathway in Arabidopsis.
Highlights
In animals, melatonin is involved in innate immunity by acting on basophils, eosinophils, eosinophils, monocytes-macrophages, neutrophils, dendritic cells, mast cells and natural killer cells[47,48]
Using the knockout mutant of serotonin N-acetyltransferase (SNAT) which is the penultimate enzyme in melatonin biosynthesis pathway, Lee et al found that snat knockout mutants exhibited susceptibility to pathogen Pst DC3000 infection that coincided with decreased endogenous melatonin and salicylic acid (SA) levels as well as reduced induction of defense genes, this indicated that melatonin-elicited pathogen resistance is SA-dependent in Arabidopsis[33]
To gain additional insight into the metabolic homeostasis which is commonly affected by exogenous melatonin and bacterial pathogen Pst DC3000 infection, comparative metabolomic analysis using GC-TOF-MS was performed to quantify the primary metabolites after stress treatments
Summary
Melatonin is involved in innate immunity by acting on basophils, eosinophils, eosinophils, monocytes-macrophages, neutrophils, dendritic cells, mast cells and natural killer cells[47,48]. Using the knockout mutant of serotonin N-acetyltransferase (SNAT) which is the penultimate enzyme in melatonin biosynthesis pathway, Lee et al found that snat knockout mutants exhibited susceptibility to pathogen Pst DC3000 (avrRpt2) infection that coincided with decreased endogenous melatonin and SA levels as well as reduced induction of defense genes, this indicated that melatonin-elicited pathogen resistance is SA-dependent in Arabidopsis[33]. Shi et al found that melatonin positively regulated plant innate immunity against bacterial pathogen in SA- and nitric oxide (NO)-dependent pathway[41]. Further studies investigated the association among sugars and sugar alcohols, melatonin-mediated disease response, and SA and NO signaling in Arabidopsis.
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