Conserved redox‐dependent DNA binding of ROXY glutaredoxins with TGA transcription factors

The Arabidopsis thaliana CC ‐type glutaredoxin ( GRX ) ROXY 1 and the bZIP TGA transcription factor ( TF ) PERIANTHIA ( PAN ) interact in the nucleus and together regulate petal development. The CC ‐type GRX s exist exclusively in land plants, and in contrast to the ubiquitously occurring CPYC and CGFS GRX classes, only the CC ‐type GRX s expanded strongly during land plant evolution. Phylogenetic analyses show that TGA TF s evolved before the CC ‐type GRX s in charophycean algae. Mp ROXY 1/2 and Mp TGA were isolated from the liverwort Marchantia polymorpha to analyze regulatory ROXY / TGA interactions in a basal land plant. Homologous and heterologous protein interaction studies demonstrate that nuclear ROXY / TGA interactions are conserved since the occurrence of CC ‐type GRX s in bryophytes and mediated by a conserved ROXY C‐terminus. Redox EMSA analyses show a redox‐sensitive binding of Mp TGA to the cis ‐regulatory as‐1‐ like element. Furthermore, we demonstrate that Mp TGA binds together with Mp ROXY 1/2 to this motif under reducing conditions, whereas this interaction is not observed under oxidizing conditions. Remarkably, heterologous complementation studies reveal a strongly conserved land plant ROXY activity, suggesting an ancestral role for CC ‐type GRX s in modulating the activities of TGA TF s. Super‐resolution microscopy experiments detected a strong colocalization of ROXY 1 with the active form of the RNA polymerase II in the nucleus. Together, these data shed new light on the function of ROXY s and TGA TF s and the evolution of redox‐sensitive transcription regulation processes, which likely contributed to adapt land plants to novel terrestrial habitats.