title: Melatonin enhances thermotolerance by promoting cellular protein protection in tomato plants.
abstract: Melatonin is a pleiotropic signaling molecule that provides physiological protection against diverse environmental stresses in plants. Nonetheless, the mechanisms for melatonin-mediated thermotolerance remain largely unknown. Here, we report that endogenous melatonin levels increased with a rise in ambient temperature and that peaked at 40°C. Foliar pretreatment with an optimal dose of melatonin (10 μmol/L) or the overexpression of N-acetylserotonin methyltransferase (ASMT) gene effectively ameliorated heat-induced photoinhibition and electrolyte leakage in tomato plants. Both exogenous melatonin treatment and endogenous melatonin manipulation by overexpression of ASMT decreased the levels of insoluble and ubiquitinated proteins, but enhanced the expression of heat-shock proteins (HSPs) to refold denatured and unfolded proteins under heat stress. Meanwhile, melatonin also induced expression of several ATG genes and formation of autophagosomes to degrade aggregated proteins under the same stress. Proteomic profile analyses revealed that protein aggregates for a large number of biological processes accumulated in wild-type plants. However, exogenous melatonin treatment or overexpression of ASMT reduced the accumulation of aggregated proteins. Aggregation responsive proteins such as HSP70 and Rubisco activase were preferentially accumulated and ubiquitinated in wild-type plants under heat stress, while melatonin mitigated heat stress-induced accumulation and ubiquitination of aggregated proteins. These results suggest that melatonin promotes cellular protein protection through induction of HSPs and autophagy to refold or degrade denatured proteins under heat stress in tomato plants.
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.|Department of Horticulture, Guizhou University, Guiyang, China.
authors.forename: Wen
authors.initials: W
authors.lastname: Xu
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.
authors.forename: Shu-Yu
authors.initials: SY
authors.lastname: Cai
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.
authors.forename: Yun
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.
authors.forename: Golam Jalal
authors.initials: GJ
authors.lastname: Ahammed
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.|Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Hangzhou, China.
authors.forename: Xiao-Jian
authors.initials: XJ
authors.lastname: Xia
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.|Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Hangzhou, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Shi
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.|Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Hangzhou, China.
authors.forename: Yan-Hong
authors.initials: YH
authors.lastname: Zhou
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China.|Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Hangzhou, China.|Key Laboratory of Horticultural Plants Growth, Development and Quality Improvement, Agricultural Ministry of China, Hangzhou, China.
authors.forename: Jing-Quan
authors.initials: JQ
authors.lastname: Yu
authors.affiliation: University of Texas Health Science Center, San Antonio, TX, USA.
authors.forename: Russel J
authors.initials: RJ
authors.lastname: Reiter
authors.affiliation: Department of Horticulture, Zhejiang University, Hangzhou, China. jie@zju.edu.cn.|Zhejiang Provincial Key Laboratory of Horticultural Plant Integrative Biology, Hangzhou, China. jie@zju.edu.cn.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhou
mesh_terms: D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018869:Heat-Shock Response / Q000187:drug effects*; D006358:Hot Temperature; D018551:Solanum lycopersicum / Q000378:metabolism*; D008550:Melatonin / Q000494:pharmacology*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
chemical_list: D018840:HSP70 Heat-Shock Proteins; D000121:Acetylserotonin O-Methyltransferase; D012273:Ribulose-Bisphosphate Carboxylase; D008550:Melatonin
keywords: 
  N-acetylserotonin methyltransferase
  ; autophagy; heat-shock proteins; melatonin; protein protection; thermotolerance; tomato