The Ca²⁺/calmodulin2‐binding transcription factor <scp>TGA</scp>3 elevates <i><scp>LCD</scp></i> expression and H₂S production to bolster Cr⁶⁺ tolerance in Arabidopsis

Abstract

Summary Heavy metal ( HM ) contamination on agricultural land not only reduces crop yield but also causes human health concerns. As a plant gasotransmitter, hydrogen sulfide (H 2 S) can trigger various defense responses and help reduce accumulation of HM s in plants; however, little is known about the regulatory mechanisms of H 2 S signaling. Here, we provide evidence to answer the long‐standing question about how H 2 S production is elevated in the defense of plants against HM stress. During the response of Arabidopsis to chromium (Cr 6+ ) stress, the transcription of L‐cysteine desulfhydrase ( LCD ), the key enzyme for H 2 S production, was enhanced through a calcium (Ca 2+ )/calmodulin2 (CaM2)‐mediated pathway. Biochemistry and molecular biology studies demonstrated that Ca 2+ /CaM2 physically interacts with the bZIP transcription factor TGA 3, a member of the ‘ TGACG ’‐binding factor family, to enhance binding of TGA 3 to the LCD promoter and increase LCD transcription, which then promotes the generation of H 2 S. Consistent with the roles of TGA 3 and CaM2 in activating LCD expression, both cam2 and tga3 loss‐of‐function mutants have reduced LCD abundance and exhibit increased sensitivity to Cr 6+ stress. Accordingly, this study proposes a regulatory pathway for endogenous H 2 S generation, indicating that plants respond to Cr 6+ stress by adjusting the binding affinity of TGA 3 to the LCD promoter, which increases LCD expression and promotes H 2 S production. This suggests that manipulation of the endogenous H 2 S level through genetic engineering could improve the tolerance of grains to HM stress and increase agricultural production on soil contaminated with HM s.