MYB156 promotes root sucker formation by repressing IDD14 and CKX1 to elevate cytokinin levels in Populus

Root suckers enable clonal propagation of rooting-recalcitrant poplars, conferring rejuvenated traits such as enhanced survival and accelerated growth. Despite widespread clonal propagation and ecological restoration, the essential genes controlling sucker development remain unidentified. MYB156 is a positive regulator of root sucker formation in white poplar (Populus davidiana × P. bolleana). MYB156 is predominantly expressed in proliferation-competent root cells, including vascular cambium and phellogen. Gain- and loss-of-function analyses demonstrated that MYB156 overexpression enhanced root suckering and secondary growth, whereas myb156 mutants were severely compromised in both. Meanwhile, cytokinin levels increased two- to fivefold in roots with MYB156 overexpression but were significantly reduced in myb156 mutant roots. MYB156 directly represses IDD14 and CKX1, reducing cytokinin catabolism and alleviating IDD14-mediated suppression of cytokinin accumulation; IDD14 RNAi lines similarly showed elevated cytokinin and enhanced suckering. Cytokinin response elements in the MYB156 promoter and MYB156 autoactivation establish a cytokinin-MYB156 positive feedback loop amplifying cytokinin signaling in meristematic zones. Live imaging with the cytokinin response reporter TCSn:RFP demonstrated that suckering in MYB156-overexpressing plants shifted from the phellogen to the vascular cambium. These findings establish a MYB156-CKX1/IDD14-cytokinin module that creates a permissive context for suckering, providing a transcriptional blueprint for clonal propagation.