Huanxin Zhang,Guoquan Li,Chengpu Yan,Xinlong Zhang,Na Cao,Meiwang Le,Xinlong Hu,Fanghong Zhu,Wenge Liu
Waterlogging is a serious abiotic stressor that drastically hinders the growth and productivity of melon (Cucumis melo) around the world, due to the reduction in available oxygen levels in the waterlogged tissues. However, the mechanism underlying the responses to waterlogging stress in melon is largely unknown. In this study, physiological and transcriptome data of the waterlogging-sensitive accession ‘L39’ and the waterlogging-tolerant accession ‘L45’ were investigated under conditions of normal water supply and waterlogging stress. The results showed that ‘L45’ exhibited higher chlorophyll contents and lower REL (relative electrolyte leakage) and MDA (malondialdehyde) contents compared with ‘L39’ under waterlogging stress. Additionally, waterlogging stress only led to the stomatal closure and chloroplast damage of ‘L39’. In total, 1748 genes were differentially expressed in the leaves of waterlogging-stressed ‘L45’ compared with control, whereas 3178 genes were differentially expressed in ‘L39’. Further analysis indicated that genes related to chlorophyll synthesis and photosynthesis were more depressed in ‘L39’, while sugar cleavage, glycolysis, and fermentation genes were highly induced in ‘L39’ compared with ‘L45’. The expression of genes involved in ROS (reactive oxygen species) scavenging and hormone signaling significantly differed between ‘L39’ and ‘L45’ in their response to waterlogging stress. Moreover, a total of 311 differentially expressed transcription factors were waterlogging-responsive, among which members of the ERF (ethylene response factor), bHLH (basic helix-loop-helix), and WRKY families might play crucial roles in waterlogging tolerance in melon. This study unraveled the molecular responses to waterlogging stress in melon and could provide helpful candidate genes for further molecular breeding of waterlogging-tolerant melon varieties.Keywords:Cucumis melo;waterlogging;transcriptome;molecular response
Melatonin (MT), polyamines (PAs), and ethylene have been suggested to play key roles in plant growth and development in response to environmental abiotic stresses. However, the effect of melatonin on polyamine and ethylene metabolism under waterlogging stress has rarely been elucidated. The main purpose of this study was to investigate the effect of melatonin pretreatment on waterlogging stress in alfalfa. The experiment was arranged into four treatment groups control with water pretreatment (CK-MT), control with melatonin pretreatment (CK+MT), waterlogging pretreated with water (WL-MT) and waterlogging pretreated with melatonin (WL+MT), with three replications. Six-week-old alfalfa seedlings were pretreated with 100 μM melatonin and exposed to waterlogging stress for 10 days. Plant growth rate, different physiological characteristics, and gene expression level were measured. Results showed that waterlogging induced melatonin accumulation, and melatonin pretreatment increased endogenous MT levels for the control and water-logged plants. Waterlogging stress caused a significant reduction in plant growth, chlorophyll content, photochemical efficiency (Fv/Fm) and net photosynthetic rate (Pn), while also causing increased leaf electrolyte leakage (EL) and malondialdehyde (MDA) content. Pretreatment with melatonin alleviated the waterlogging-induced damage and reduction in plant growth, chlorophyll content, Fv/Fm and Pn. Waterlogging stress significantly increased leaf polyamines (Put, Spd, Spm) and ethylene levels, and the increased PAs and ethylene levels are coupled with higher metabolic enzymes and gene expressions. While pretreatment with melatonin further increased Put, Spd and Spm levels, it also decreased ethylene levels under waterlogging, and those increased PAs levels or decreased ethylene levels are regulated by the metabolic enzymes and gene expressions. The results in this study provide more comprehensive insight into the physiological and molecular mechanisms of melatonin-improved waterlogging tolerance in alfalfa. Furthermore, they suggested that melatonin improved waterlogging tolerance in alfalfa at least partially by reprogramming ethylene and PA biosynthesis, attributable to the increased PAs and decreased ethylene levels, which leads to more enhanced membrane stability and photosynthesis as well as less leaf senescence caused by ethylene.
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