Spatiotemporal Dissection of the Infection Response to Bacterial Soft Rot in Non-heading Chinese cabbage.

Bacterial soft rot caused by Pectobacterium brasiliense (Pbr) leads to substantial yield losses in cruciferous vegetables, including non-heading Chinese cabbage (pak choi, Brassica rapa subsp. chinensis). This study employed an integrated physiological and multi-tissue transcriptomic approach to decipher the infection response strategies of pak choi against Pbr. Age-dependent resistance was detected, with susceptibility decreasing as plants matured. In susceptible four-week-old plants, Pbr infection induced oxidative stress, characterized by the accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), and activated a multi-layered response system involving key antioxidant enzymes (SOD, POD, CAT, APX) and phenylpropanoid pathway enzymes (PAL, PPO). Transcriptome profiling revealed a tissue-specific division of response labor. Petioles, the primary infection site, mounted a response characterized by a bidirectional reprogramming of the ribosomal pathway and activation of sulfur metabolism, including the upregulation of cysteine synthesis genes (cysC, cysK). In contrast, leaves implemented a resource-reallocation strategy, involving broad suppression of photosynthesis and hormonal rebalancing-specifically, upregulation of JA repressors (JAZ) and downregulation of the SA signaling component NPR1. Furthermore, we identified an infection-induced transcriptional regulatory network mediated by transcription factors (e.g., MYB, WRKY, AP2-EREBP, NAC), and weighted gene co-expression network analysis (WGCNA) pinpointed hub TFs in infection-associated and health-associated modules. Our findings provide a comprehensive framework for age-dependent and tissue-coordinated infection response in pak choi, offering valuable genetic targets for breeding resistance against bacterial soft rot.