Abstract
Soil salinization severely constrains the productivity of Medicago sativa L. Although exogenous melatonin (MT) has been proven to effectively alleviate salt stress injury in plants, the molecular regulatory networks underlying its function during the early stages of stress response remain not fully elucidated. In this study, we systematically investigated the specific regulatory mechanisms of exogenous MT-mediated salt tolerance in alfalfa seedlings during the early phase (12–24 h) of salt stress by integrating physiological, biochemical, and transcriptomic analyses. The results showed that MT treatment significantly inhibited membrane lipid peroxidation (indicated by decreased MDA content) in leaves and upregulated the activities of antioxidant enzymes as well as the levels of osmoprotectants, such as soluble sugars. Transcriptomic (RNA-seq) analysis revealed that MT induced a precise strategy of temporal transcriptional reconfiguration. At the initial stage of stress (12 h), MT preferentially downregulated the expression of genes related to ribosome biogenesis and chromatin remodeling. This transcriptional suppression suggests that plants adopted an “energy saving strategy,” aiming to minimize basal metabolic consumption and potentially reallocate limited energy resources toward the antioxidant defense system. Subsequently, at 24 h, MT orchestrated the comprehensive activation of the ABA signaling cascade and secondary metabolic pathways, such as phenylpropanoid and flavonoid biosynthesis, thereby establishing a long-term chemical defense barrier. Furthermore, weighted gene co-expression network analysis (WGCNA) identified ABF2 and Susy as key hub genes mediating soluble sugar accumulation. This study elucidates the molecular basis by which melatonin enhances early salt tolerance in alfalfa through a temporal transition from an “energy-saving” strategy to “active defense,” providing new theoretical insights for the molecular breeding of stress resistance in leguminous forage crops.
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Claims 8
Claim · model-written summary
Melatonin reduced leaf MDA content under salt stress.
- Taxon
- Alfalfa
Medicago sativat0 - Treatment
- MT treatmente0
- Outcome
- MDA contente0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“MT treatment significantly inhibited membrane lipid peroxidation (indicated by decreased MDA content) in leaves”
t0“Alfalfa”
Claim · model-written summary
Melatonin increased antioxidant enzyme activities under salt stress.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- Exogenous Melatonint0
- Outcome
- activities of antioxidant enzymese0
- Direction
- upregulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“upregulated the activities of antioxidant enzymes as well as the levels of osmoprotectants, such as soluble sugars.”
t0“Exogenous Melatonin Enhances Salt Tolerance in Alfalfa”
Claim · model-written summary
Melatonin increased soluble sugar levels under salt stress.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- Exogenous Melatonint0
- Outcome
- levels of osmoprotectants, such as soluble sugarse0
- Direction
- upregulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“upregulated the activities of antioxidant enzymes as well as the levels of osmoprotectants, such as soluble sugars.”
t0“Exogenous Melatonin Enhances Salt Tolerance in Alfalfa”
Claim · model-written summary
At 12 h, melatonin downregulated ribosome biogenesis genes.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- MTe0
- Outcome
- expression of genes related to ribosome biogenesise0
- Direction
- downregulatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At the initial stage of stress (12 h), MT preferentially downregulated the expression of genes related to ribosome biogenesis and chromatin remodeling.”
t0“Alfalfa”
Claim · model-written summary
At 12 h, melatonin downregulated chromatin remodeling genes.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- MTe0
- Outcome
- chromatin remodelinge0
- Direction
- downregulatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At the initial stage of stress (12 h), MT preferentially downregulated the expression of genes related to ribosome biogenesis and chromatin remodeling.”
t0“Alfalfa”
Claim · model-written summary
At 24 h, melatonin activated ABA signaling.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- MTe0
- Outcome
- ABA signaling cascadee0
- Direction
- activatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at 24 h, MT orchestrated the comprehensive activation of the ABA signaling cascade and secondary metabolic pathways”
t0“Alfalfa”
Claim · model-written summary
At 24 h, melatonin activated secondary metabolic pathways.
- Taxon
- AlfalfaMedicago sativat0
- Treatment
- MTe0
- Outcome
- secondary metabolic pathways, such as phenylpropanoid and flavonoid biosynthesise0
- Direction
- activatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at 24 h, MT orchestrated the comprehensive activation of the ABA signaling cascade and secondary metabolic pathways, such as phenylpropanoid and flavonoid biosynthesis”
t0“Alfalfa”
Claim · model-written summary
ABF2 and Susy were identified as hub genes mediating soluble sugar accumulation.
- Taxon
- AlfalfaMedicago sativat0
- Gene
- ABF2 and Susye0
- Outcome
- soluble sugar accumulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“weighted gene co-expression network analysis (WGCNA) identified ABF2 and Susy as key hub genes mediating soluble sugar accumulation.”
t0“Alfalfa”
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