Transcriptome and metabolome analysis reveals key genes and secondary metabolites of Casuarina casuarina in response to drought stress

Abstract Casuarina equisetifolia is drought resistant, salt resistant, and able to grow in barren environments. It is often used to reduce wind damage, to prevent sand erosion, and to help establish plant communities in tropical and subtropical coastal zones. To determine the basis for its drought resistance, we conducted transcriptomic and metabolic analyses of young branchlets under a non-drought treatment (D_0h) and 2-, 12-, and 24-h-long drought treatments (D_2h, D_12h, and D_24h). A total of 5033 and 8159 differentially expressed genes were identified in D_0h/D_2h and D_0h/D_24h. These DEGs are involved in plant hormone signal transduction, jasmonic acid biosynthesis, flavonoid biosynthesis, and phenylalanine biosynthesis. A total of 148 and 168 differentially accumulated metabolites were identified in D_0h/D_12h and D_0h/D_24h. These differentially accumulated metabolites are mainly amino acids, phenolic acids, and flavonoids. In conclusion, C. equisetifolia responds to drought by regulating plant hormone signal transduction and the biosynthesis of JA, flavonoids, and phenylpropane. These results increase the understanding of drought resistance in C. equisetifolia and provide new insights into coastal vegetation reconstruction and management.