<scp>RABBIT EARS</scp> directly regulates <i>WOX4</i> transcription and inhibits secondary growth in Arabidopsis stem

Plant secondary growth drives stem thickening and biomass accumulation, but its regulation is not yet fully understood. We have identified a novel semi-dominant mutant, rbe-d, characterized by a significant reduction in cambium cells and a complete absence of secondary growth in interfascicular regions in the stem. Gene cloning experiments indicated that the activation of the C2H2 zinc finger transcription factor, AT5G06070/RABBIT EARS (RBE), is responsible for the rbe-d phenotype. Transgenic analysis confirmed that overexpression of RBE represses secondary growth, while the rbe-2 mutant increased the width of the interfascicular cambium-derived (ICD) region. The RBE gene is expressed in the procambium and cambium regions. Transcriptomic analysis showed that genes of the tracheary element differentiation inhibitory factor-phloem intercalated with xylem (TDIF-PXY) central regulatory pathway are repressed in the rbe-d mutant plants. Biochemical analyses confirmed that RBE binds directly to the promoter of WUSCHEL-related homeobox (WOX4), a TDIF-PXY downstream WOX gene that regulates cambium cell proliferation. Moreover, genetic analysis confirmed that WOX4 is epistatic to RBE in secondary growth. Our results indicate that RBE inhibits cambium proliferation and thereby impacts secondary growth by directly repressing WOX4. These findings offer valuable new insight into the regulation of secondary growth in the Arabidopsis stem.