SaWRKY40 mediates betacyanin biosynthesis and enhances salt tolerance in Suaeda australis

Coastal halophytes thrive in saline habitats and provide valuable models for uncovering the mechanisms underlying salt tolerance. Suaeda australis (R. Br.) Moq., a halophytic species, exhibits remarkable salt tolerance accompanied by leaf betacyanin accumulation, yet its molecular basis remains unclear. Integrating physiological, metabolomic, and transcriptomic analyses, SaWRKY40 was identified as a key transcription factor that directly regulates SaCYP76AD1 , a cytochrome P450 gene in the betanin biosynthetic pathway. Under high salinity, SaWRKY40 expression was strongly induced, activating SaCYP76AD1 transcription and enhancing the conversion of L -tyrosine to L -DOPA, leading to substantial betacyanin accumulation. This was accompanied by increased antioxidant enzyme activities (SOD and CAT) and reduced ROS levels (O 2 •⁻ , H₂O₂), indicating improved redox balance under salt stress. A proposed mechanistic model suggested that salt stress triggers SaWRKY40, which transcriptionally activates SaCYP76AD1 to promote betacyanin accumulation. The accumulated betacyanin promoted ROS scavenging, stabilizing cellular redox homeostasis and mitigating oxidative damage. This SaWRKY40- SaCYP76AD1 regulatory module supports a novel link between betacyanin and salt tolerance in halophytes. • Salt stress induces betacyanin accumulation and maintains ROS homeostasis in Suaeda australis . • SaWRKY40 is a salt-responsive transcription factor positively regulating betacyanin biosynthesis. • SaWRKY40 directly activates SaCYP76AD1 to enhance betanin pathway flux. • Betacyanin accumulation improves salt tolerance via enhanced ROS scavenging capacity.