title: Chloroplastic biosynthesis of melatonin and its involvement in protection of plants from salt stress.
abstract: 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 recently-discovered 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 Kmand Vmaxof the purified recombinant MzASMT9 protein for melatonin synthesis were 500 μM and 12 pmol/min·mg protein, respectively. Arabidopsis ectopically-expressing 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 highly-expressed 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.
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Xiaodong
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Department of Cellular &Structural Biology, The UT Health Science Center, San Antonio, TX, USA.
authors.forename: Dun X
authors.initials: DX
authors.lastname: Tan
authors.affiliation: Plant &Food Research, Private Bag 92169, Auckland, New Zealand.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Allan
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Bixiao
authors.initials: B
authors.lastname: Zuo
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Department of Cellular &Structural Biology, The UT Health Science Center, San Antonio, TX, USA.
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: College of Biological Sciences, China Agricultural University, Beijing, China.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Wang
authors.affiliation: College of Biological Sciences, China Agricultural University, Beijing, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Guo
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Jingzhe
authors.initials: J
authors.lastname: Zhou
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Dongqian
authors.initials: D
authors.lastname: Shan
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Qingtian
authors.initials: Q
authors.lastname: Li
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Zhenhai
authors.initials: Z
authors.lastname: Han
authors.affiliation: College of Horticulture, China Agricultural University, Beijing, China.
authors.forename: Jin
authors.initials: J
authors.lastname: Kong
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000528:radiation effects; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D018533:Biomass; D002736:Chloroplasts / Q000378:metabolism* / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008315:Malondialdehyde / Q000378:metabolism; D027845:Malus / Q000235:genetics / Q000528:radiation effects; D008550:Melatonin / Q000096:biosynthesis*; D010788:Photosynthesis / Q000528:radiation effects; D010802:Phylogeny; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D030821:Plants, Genetically Modified; D017382:Reactive Oxygen Species / Q000378:metabolism; D055049:Salt Tolerance / Q000187:drug effects / Q000528:radiation effects; D012965:Sodium Chloride / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects*; D015854:Up-Regulation / Q000235:genetics / Q000528:radiation effects
chemical_list: D010940:Plant Proteins; D017382:Reactive Oxygen Species; D049452:Green Fluorescent Proteins; D012965:Sodium Chloride; D008315:Malondialdehyde; D008550:Melatonin