Brassinosteroids negatively regulate plant de novo root regeneration

De novo root regeneration (DNRR) is essential for plant survival under mechanical damage and agricultural productivity, and plant hormones play a pivotal role in this process. While auxin, jasmonate (JA), and ethylene are known to be involved in DNRR, the role of brassinosteroids (BR) remains unreported. This study reveals that the reduced BR signaling promotes DNRR, whereas elevated BR signaling suppresses DNRR. Then we further validate that this mechanism is conserved across diverse plant species, including Brassica napus, Nicotiana benthamiana, and Solanum lycopersicum. Studies on the regulatory mechanism indicate that BR regulates DNRR by modulating auxin-related pathways. BR induces the transcription factor BZR1, which directly represses auxin transporter genes (PIN1 and PIN3), thereby reducing auxin levels at the wound sites of leaf explants and inhibiting root primordia formation. Besides, BZR1 also transcriptionally suppresses root meristem initiation-related genes (WOX5 and LBD16) to inhibit DNRR. This study demonstrates BR function in plant DNRR, refines the network of hormonal regulation of DNRR, and provides an important clue for improving plant rooting efficiency in agriculture.