BZR1 promotes pluripotency and callus formation through direct regulation of ARF7 & ARF19

Plants have the remarkable ability to regenerate whole organisms through formation of pluripotent cell masses from somatic cells. Cellular programs leading to fate change resemble lateral root (LR) formation and are chiefly regulated by auxin. Brassinosteroid signalling also plays an important role in LR formation, but little is known about the direct link between auxin and brassinosteroid components, such as BZR1 and BES1, in pluripotency acquisition. Here we show that gain-of-function mutants bzr1-D and bes1-D exhibit altered callus formation, yet disruption of these transcription factors does not cause major changes to callus formation or de novo organogenesis. Moreover, our data reveal that BZR1 displays enhanced expression in callus tissue and directly binds to the promoters of ARF7 and ARF19, two master pluripotency regulators, leading to their enhanced transcription. Remarkably, callus formation is abrogated in bzr1-D upon disruption of these ARFs, emphasizing that the callus phenotype of BZR1 depends on these auxin-signalling components. In conclusion, we depict a link between ARF7, ARF19, and BZR1 in promoting pluripotency acquisition, portraying BZR1 as a major supporting factor in callus formation.