Multi-omics reveals phenol-based coordinated defense of Sparganium stoloniferum rhizoma

Sparganium stoloniferum is a widely distributed aquatic medicinal plant that exhibits exceptional tolerance to environmental stress. Interestingly, the phenols in S. stoloniferum which have medicinal properties, are defensive compounds. Studies integrating transcriptome, proteome, and metabolome analyses have highlighted the phenylpropanoid and flavonoid biosynthesis pathways, which are related to the defense mechanisms of S. stoloniferum. During the growth process, S. stoloniferum rhizoma (SL) accumulates lignin, forming a physical defense, and phenylpropanoids and flavonoids derived during the lignin biosynthesis process provide chemical defense. In this study, a map of the molecular processes involved in the coordinated defense of S. stoloniferum was generated. The expression patterns of genes involved in the coordinated defense of SL were consistent with the omics results. The cDNA of the phenylalanine ammonia-lyase (PAL) gene from S. stoloniferum (SsPAL) was cloned. The recombinant protein SsPAL showed good affinity and catalytic activity for L-phenylalanine. Heat stress experiments indicated that genes related to phenol biosynthesis were upregulated when S. stoloniferum responded to stress. Therefore, phenols played a crucial defense role when S. stoloniferum was at an early developmental stage or responded to stress in a short time. In contrast, the physical defense mainly relied on lignin formation, which was the main defense mechanism of SL in the late growth stage. Based on these results, we discuss the causes of phenolic pharmacological substance formation in medicinal aquatic plants. These results provide new insights into the defense strategies of aquatic plants.