Insights Into the Regulation of Salt Tolerance by Flavonoid and Cyanoamino Acid Metabolism in Sorghum‐Sudangrass Hybrids

Clarifying the molecular mechanisms underlying salt tolerance in high‐performing sorghum‐sudangrass hybrids can aid the identification of salt tolerance genes. Here, the previously screened salt‐tolerant sorghum‐sudangrass hybrid variety MN9 and the salt‐sensitive variety MN4 were grown in sand‐filled pots. At the five‐leaf stage (21 days after sowing), seedlings were subjected to NaCl solutions at six concentrations (0, 70, 140, 210, 280, and 350 mM). After 72 h of treatment, mature leaves were collected to determine physiological indices across all concentrations. We then conducted transcriptome sequencing of leaf samples from the 0 mM (control) and 280 mM (high salt stress) treatments, and the sequencing results were validated by qRT‐PCR. Under salt stress, MN9 maintained a high relative chlorophyll content (SPAD value), accumulated significantly more proline than MN4, and showed high peroxidase (POD) activity throughout the treatment period. Transcriptome profiling revealed 4340 differentially expressed genes (DEGs) between the salt‐tolerant and salt‐sensitive varieties under salt stress, including 2624 upregulated and 1716 downregulated genes. KEGG enrichment analysis showed that, under control conditions, genes in both varieties were enriched in the photosynthesis pathway; SORBI_3001G147400 ( petF ) supported normal photosynthetic function. Following salt stress, DEGs were predominantly enriched in biosynthesis of secondary metabolites, cyanoamino acid metabolism, and flavonoid biosynthesis. Key flavonoid biosynthesis genes (e.g., CHS , CYP98A , and CYP75B1 ) were specifically induced. In the cyanoamino acid metabolism pathway, SORBI_3004G335500 ( HNL ) and SORBI_3001G012400 ( UGT85B1 ) were strongly expressed in MN9. The hydroxynitrile lyase gene HNL (SORBI_3004G335500) was experimentally verified as a key regulator of salt tolerance in sorghum‐sudangrass hybrid.