High Expression of CpMAPK9 Increased Jasmonic Acid Levels Potentially Improving Root Rot Resistance in Codonopsis pilosula
Background: This study aimed to investigate the molecular mechanisms underlying the response of Codonopsis pilosula roots to Fusarium oxysporum infection, which causes root rot and significant economic losses, and to provide a theoretical basis for breeding resistant varieties and developing effective control strategies. Methods: Root samples of C. pilosula were inoculated with F. oxysporum and harvested across five distinct intervals (0, 6, 24, 72, and 120 h after inoculation). Transcriptome sequencing was performed on 15 samples, generating 171.65 GB of clean data. De novo assembly was used to construct unigenes, followed by functional annotation and differential expression analysis. In addition, CpMAPK9 was transiently overexpressed in C. pilosula leaves to evaluate its role in jasmonic acid (JA) biosynthesis and disease resistance. Results: A total of 94,896 unigenes were obtained. Functional analysis showed that genes involved in hormone signal transduction, the MAPK signaling pathway, and plant–pathogen interactions were consistently activated in response to infection. Among the MAPK gene family, CpMAPK9 showed significant expression changes. Transient overexpression of CpMAPK9 significantly increased JA accumulation, indicating that CpMAPK9 positively regulates JA biosynthesis and may enhance resistance to root rot. Conclusions: In conclusion, our findings indicate that CpMAPK9 actively modulates JA-mediated defense pathways in C. pilosula during F. oxysporum invasion. Our findings shed light on the intricate molecular networks that drive disease defense, offering valuable theoretical insights to guide subsequent crop improvement initiatives.