Melatonin enhances thermotolerance by promoting cellular protein protection in tomato plants.
J Pineal Res. 2016 Aug 2. Epub 2016 Aug 2. PMID: 27484733
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 μM) 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. Aggegation responsive proteins such as HSP70 and Rubisco activase were preferentially accumulated and ubiquitinated in wild-type plants under heat stress, whilst 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. This article is protected by copyright. All rights reserved.