Objective To explore defense genes and metabolic pathways influencing post-germination growth of Madhuca hainanensis seeds.

Method The changes of fresh weight of seeds and seedling height of M. hainanensis after exogenous salicylic acid (SA) treatment were determined. Combined with Illumina transcriptome and targeted metabolomics, correlation analysis between differentially expressed genes and metabolic pathways was conducted. Weighted gene co-expression network analysis (WGCNA) and validation of key defense genes were performed.

Result Under exogenous SA treatment, the fresh weight change rate of seeds and seedling height growth rate of M. hainanensis were lower than those in the blank control group by 1.47 and 1.68 percentage points, respectively. Defense-related plant hormones such as SA and jasmonic acid, and abundant secondary metabolites accumulated in the five-leaf-stage seedlings of M. hainanensis. Meanwhile, numerous defense-related pathways were activated, including plant-pathogen interaction, plant hormone signal transduction, MAPK signaling pathway-plant, and biosynthesis of secondary metabolites. NFP, RIN4, PK1, WRKY17 and WRKY53 were identified as key defense genes enriched in the plant-pathogen interaction pathway.

Conclusion Exogenous SA affects post-germination growth of M. hainanensis seeds, and the five-leaf-stage seedlings initiate defense mechanisms with key defense genes mainly enriched in the plant-pathogen interaction pathway. This study provides a theoretical foundation for analyzing the potential mechanisms underlying the slow growth of M. hainanensis seedings.