Vascular bundle plasticity and cellular heterogeneity drive asymmetric carbon partitioning in maize nodes

Plants optimize carbon partitioning in response to heterogeneous nutrient availability to enhance resource acquisition. However, the structural and molecular mechanisms underlying this plasticity remain poorly understood. Here, we combined histology, fluorescent tracing, and single-cell RNA sequencing to investigate how maize basal nodes mediate asymmetric carbon allocation under split-root heterogeneous phosphorus (P) supply. We found that the P-supplied side exhibited significant increases in the number and cross-sectional area of vascular bundles, particularly small vascular bundles and phloem, accompanied by elevated non-structural carbohydrate levels and enhanced photoassimilate allocation. Single-cell transcriptomics identified 13 cell types and revealed cell-type-specific transcriptional reprogramming, including upregulation of carbohydrate metabolism (e.g., incw1, invan5) and transport genes (e.g., sweet13a, stp2, stp4). Pseudotime analysis indicated a differentiation bias toward xylem parenchyma under local P supply. Additionally, downregulation of trpp14 in procambial cells suggests a potential role for trehalose-6-phosphate in regulating sink strength. Our study establishes vascular bundle plasticity and cellular functional heterogeneity as key mechanisms for spatially programmed carbon partitioning in response to P heterogeneity, providing insights for improving nutrient use efficiency in crops.