Abstract
Background
Methyl jasmonate (MeJA) plays a key role in enhancing plant resistance to a wide range of diseases. However, the specific defense responses it induced and the underlying molecular mechanisms remain incompletely understood in many plant-pathogen systems. This study aimed to determine whether exogenous MeJA enhances resistance to leaf spot disease caused by Alternaria tenuissima in peony (Paeonia lactiflora) and to elucidate the associated molecular and biochemical mechanisms through integrated transcriptomic and biochemical analyses.Results
Compared with the control (CK), pretreatment with 25-75 µmol L- 1 MeJA significantly reduced disease severity, with 75 µmol L- 1 identified as the optimal concentration. Peony leaves pretreated with this concentration exhibited a stronger hypersensitive response than the CK, with initial differentiation observed at 24 h after inoculation. Transcriptome sequencing analysis identified 1,017 differentially expressed genes between the MeJA-pretreated and CK groups, primarily associated with cell wall organization, phenylpropanoid biosynthesis, terpenoid backbone biosynthesis, and flavonoid biosynthesis pathways. MeJA pretreatment up-regulated the genes involved in phenylpropanoid and lignin biosynthesis, including peroxidase 27 (POD27) and caffeic acid 3-O-methyltransferase (COMT), as well as flavonoid-related genes such as chalcone isomerase (CHI). Genes regulating pectin methylesterification, including pectin methylesterase (PME) and PME inhibitor (PMEI), were also modulated. In addition, transcription factors such as basic leucine zipper (bZIP) and heat shock transcription factor (HSF) were activated. Biochemical analyses confirmed increased levels of major cell wall components (lignin, cellulose, hemicellulose, and pectin) and total flavonoids were significantly higher in MeJA-pretreated plants compared with CK plants. A putative model of MeJA-induced defense responses against A. tenuissima was proposed.Conclusions
Exogenous MeJA pretreatment enhances resistance to leaf spot disease caused by A. tenuissima in peony by promoting cell wall reinforcement and flavonoid accumulation. These findings highlight the potential of MeJA as a strategy for managing leaf spot disease in peony cultivation.