The bHLH121-CAT2 module maintains root tip redox homeostasis to confer salt tolerance additively with the SOS pathway in Arabidopsis

Loss of bHLH121 in Arabidopsis causes pronounced salt-stress hypersensitivity, with severely impaired primary root elongation and reduced seedling biomass.

• Why it matters: Soil salinity limits essential minerals like iron, but how iron-regulated programs integrate with salt tolerance—especially via root redox control—remains unclear.
• What they did: The study used transcriptomic and histochemical analyses to show bHLH121 is needed for reactive oxygen species homeostasis in root tips under salt stress, and identified CAT2 as a direct downstream target.
• The result: CAT2 overexpression fully rescues bhlh121 salt hypersensitivity, and bhlh121 acts independently of the SOS pathway since sos2 bhlh121 double mutants show additive salt sensitivity.

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