Cell-type-specific defense priming and NHP-dependent systemic immunity against Pectobacterium in Chinese cabbage

Defense priming is an effective strategy for mounting the defensive capacity of plants. Primed plants undergo minimal changes, enabling rapid, robust responses to subsequent pathogen attack. The cell-type-specific mechanisms underlying priming and systemic immunity remain unclear. Using single-nucleus RNA sequencing (snRNA-seq), we reveal how primed Chinese cabbage coordinates N-hydroxypipecolic acid (NHP)-dependent systemic immunity against Pectobacterium carotovorum. NHP accumulates as a phloem-mobile priming signal. snRNA-seq identified a priming-specific epidermal cell state transition and transcriptional cascade: BrWRKY18-1 activates BrWRKY33-1 expression during priming, initiating NHP-dependent systemic immunity. At post-challenge primed state, pathogenesis-related genes (PRs), such as BrPR3, BrPR4-1, and BrPR4-2, are predominantly expressed in systemic tissues to inhibit infection. Notably, the functionality of these PR genes in immunity necessitates their expression in all cells to effectively enhance defensive resistance. This NHP-transcription factor-PR axis couples mobile signaling to systemic immunity, elucidating cell-type-specific defense priming.