The transcription factor BRN2 confers cadmium tolerance by regulating SAM1 expression in Arabidopsis

Cadmium (Cd) adversely affects plant growth and human health. However, the precise mechanisms through which plants adapt to and tolerate Cd toxicity remain unclear. Here, we identified a NAM, ATAF1/2, and CUC2 (NAC) transcription factor, BEARSKIN2 (BRN2), that is crucial in regulating Cd tolerance in Arabidopsis thaliana. Four-week-old wild-type (WT), brn2 mutants, sam1 mutants, brn2-1:SAM1-OX lines were exposed to hydroponic cultures in solutions with or without 50 μM Cd for 7 days. Yeast one-hybrid (Y1H) analysis indicated a putative interaction between BRN2 and S-adenosylmethionine synthase 1 (SAM1). Dual-luciferase (LUC), and Chromatin Immunoprecipitation (ChIP) assay analysis confirmed that BRN2 directly increased SAM1 transcript levels. Loss of BRN2 function caused increased Cd sensitivity and accumulation, while overexpression of BRN2 caused a Cd-resistant phenotype and lower Cd accumulation. The sam1 mutant exhibited higher Cd accumulation compared to the WT and displayed increased susceptibility to Cd stress, and brn2-1 ×sam1 double mutant showed Cd sensitivity similar to that of the sam1 mutant, while the overexpression of brn2 mutant rescued Cd tolerance and exhibited lower Cd accumulation, indicating that BRN2 contributes to Cd tolerance by facilitating SAM1 expression. Here, by examining the NAC family mutants that exhibit Cd resistance, we showed that BRN2 directly interacts with the NACRS regions of the SAM1 promoters and functions as a transcriptional activator to enhance Cd sensitivity.