The transcription factor GmbZIP131 enhances soybean salt tolerance by regulating flavonoid biosynthesis

Detoxifying reactive oxygen species (ROS) that accumulate under saline conditions is crucial for plant salt tolerance. The salt overly sensitive (SOS) pathway functions upstream, while flavonoids act downstream, in ROS scavenging under salt stress. However, the potential crosstalk between the SOS pathway and flavonoids in regulating salt stress responses and the associated mechanisms remain largely unexplored. To assess this possible connection, we investigated the role of the soybean (Glycine max) transcription factor GmbZIP131 in enhancing salt tolerance by modulating ROS homeostasis through flavonoid biosynthesis. GmSOS2 like (GmSOS2L), a key component of the SOS pathway, phosphorylates and activates GmbZIP131, thus promoting GmICHG (isoflavone conjugate-specific beta-glucosidase) expression. Metabolic profiling of transgenic soybean lines revealed that GmbZIP131 upregulates the levels of lupiwighteone and its 7-glucoside precursor, likely processed by GmICHG. Furthermore, overexpression of GmSOS2L, GmbZIP131, or GmICHG enhances the accumulation of lupiwighteone and its 7-glucoside precursor, as well as soybean salt stress tolerance. Our findings reveal a GmSOS2L-GmbZIP131-GmICHG signaling cascade that enhances soybean salt tolerance through flavonoid accumulation. This research uncovers a mechanism linking the SOS pathway to flavonoid metabolism, offering insights for improving soybean stress tolerance and advancing the molecular breeding of salt-tolerant varieties.