Melatonin is a well-known molecule which possesses many beneficial effects on human health. Many agriculture products provide natural melatonin in the diet. Cherry is one such fruit as they are rich in melatonin. In order to understand the biological roles of melatonin in cherry fruit, melatonin synthesis and its changes over 24 hr period were systematically monitored both during their development and in the ripe cherries in two cultivars, 'Hongdeng' (Prunus avium L. cv. Hongdeng) and 'Rainier' (Prunus avium L. cv. Rainier). It was found that both darkness and oxidative stress induced melatonin synthesis, which led to dual melatonin synthetic peaks during a 24 hr period. The high levels of malondialdehyde induced by high temperature and high intensity light exposure were directly related to up-regulated melatonin production. A primary function of melatonin in cherry fruits is speculated to be as an antioxidant to protect the cherry from the oxidative stress. Importantly, plant tryptophan decaboxylase gene (PaTDC) was identified in cherry fruits. Our data shows that PaTDC expression is positively related to the melatonin production in the cherry. This provides additional information to suggest that tryptophan decaboxylase is a rate-limiting enzyme of melatonin synthesis in plants.
In animals, the melatonin biosynthesis pathway has been well defined after the isolation and identification of the four key genes that are involved in the conversion of tryptophan to melatonin. In plants, there are special alternative catalyzing steps, and plant genes share very low homology with the animal genes. It was of interest to examine the phenotype of transgenic Micro-Tom tomato plants overexpressing the homologous sheep oAANAT and oHIOMT genes responsible for the last two steps of melatonin synthesis. The oAANAT transgenic plants have higher melatonin levels and lower indoleacetic acid (IAA) contents than control due to the competition for tryptophan, the same precursor for both melatonin and IAA. Therefore, the oAANAT lines lose the 'apical dominance' inferring that melatonin likely lacks auxin activity. The significantly higher melatonin content in oHIOMT lines than oAANAT lines provides new proof for the important role of ASMT in plant melatonin synthesis. In addition, the enhanced drought tolerance of oHIOMT lines will also be an important contribution for plant engineering.
Within the chloroplasts reactive oxygen species (ROS) are generated during photosynthesis and stressful conditions. Excessive ROS damages chloroplasts and reduces photosynthesis if not properly detoxified. In this current study, we document that chloroplasts produce melatonin, a recentlydiscovered plant antioxidant molecule. When N-acetylserotonin, a substrate for melatonin synthesis, was fed to purified chloroplasts, they produced melatonin in a dose-response manner. To further confirm this function of chloroplasts, the terminal enzyme for melatonin synthesis, N-acetylserotonin-O-methyltransferase (ASMT), was cloned from apple rootstock, Malus zumi. The in vivo fluorescence observations and Western blots confirmed MzASMT9 was localized in the chloroplasts. A study of enzyme kinetics revealed that the K m and V max of the purified recombinant MzASMT9 protein for melatonin synthesis were 500 μM and 12 pmol/min·mg protein, respectively. Arabidopsis ectopicallyexpressing MzASMT9 possessed improved melatonin level. Importantly, the MzASMT9 gene was found to be upregulated by high light intensity and salt stress. Increased melatonin due to the highlyexpressed MzASMT9 resulted in Arabidopsis lines with enhanced salt tolerance than wild type plants, as indicated by reduced ROS, lowered lipid peroxidation and enhanced photosynthesis. These findings have agricultural applications for the genetic enhancement of melatonin-enriched plants for increasing crop production under a variety of unfavorable environmental conditions.Chloroplasts are critically important plant cellular organelles with the major function of performing photosynthesis. The chlorophyll pigments in chloroplasts capture energy from photons, with this energy being used to synthesize organic molecules from carbon dioxide via the Calvin cycle. Large quantities of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated during photosynthesis, especially under the stressful conditions such as exposure to excessive light intensity, heat, salt, cold, drought and environmental pollutants 1-4 . ROS and RNS, if not properly detoxified, damages chloroplasts and reduces their photosynthetic efficiency, ultimately killing the cell. This damage is referred to as oxidative stress. During evolution, plants developed an array of mechanisms to protect themselves against oxidative stress 5 . One mechanism is the production of antioxidants; which include ascorbic acid, carotenoids, tocopherol, glutathione and polyphenols 6 . Interestingly another antioxidant, melatonin, initially thought to be exclusively an animal hormone, was identified in plants in 1995 7,8 . Since then melatonin has been detected in many different species of plants and plant products [9][10][11][12][13] . The significance of melatonin in plants is related to its potent free radical scavenging and antioxidant capacity [14][15][16][17] . In contrast to several other antioxidants, melatonin can enter every sub-cellular compartment due to its amphiphilic nature 16 . In addition, melaton...
Glomerella leaf spot (GLS), a fungal disease caused by Colletotrichum fructicola (C. fructicola), severely affects apple quality and yield, yet few resistance genes have been identified in apple (Malus domestica Borkh.). Here we found a transcription factor MdWRKY17 significantly induced by C. fructicola infection in the susceptible apple cultivar ‘Gala’. MdWRKY17 overexpressing transgenic ‘Gala’ plants exhibited increased susceptibility to C. fructicola, whereas MdWRKY17 RNA-interference plants showed opposite phenotypes, indicating MdWRKY17 acts as a plant susceptibility factor during C. fructicola infection. Furthermore, MdWRKY17 directly bound to the promoter of the salicylic acid (SA) degradation gene Downy Mildew Resistant 6 (MdDMR6) and promoted its expression, resulting in reduced resistance to C. fructicola. Additionally, Mitogen-activated protein kinase 3 (MdMPK3)directly interacted with and phosphorylated MdWRKY17. Importantly, predicted phosphorylation residues in MdWRKY17 by MAPK kinase 4 (MdMEK4)-MdMPK3 were critical for the activity of MdWRKY17 to regulate MdDMR6 expression. In the six susceptible germplasms, MdWRKY17 levels were significantly higher than the six tolerant germplasms after infection, which corresponded with lower SA content, confirming the critical role of MdWRKY17-mediated SA degradation in GLS tolerance. Our study reveals a rapid regulatory mechanism of MdWRKY17, which is essential for SA degradation and GLS susceptibility, paving the way to generate GLS resistant apple.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.