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

Abstract

Summary 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.