ABSTRACT
Chrysanthemum Fusarium wilt is a soil-borne disease that causes serious economic losses to the chrysanthemum industry. However, the molecular mechanism underlying the response of chrysanthemum WRKY to Fusarium oxysporum infection remains largely unknown. In this study, we isolated CmWRKY6-1 from chrysanthemum 'Jinba' and identified it as a transcriptional repressor localized in the nucleus via subcellular localization and transcriptional activation assays. We found that CmWRKY6-1 negatively regulated resistance to F. oxysporum and affected reactive oxygen species (ROS) and salicylic acid (SA) pathways using transgenic experiments and transcriptomic analysis. Moreover, CmWRKY6-1 bound to the W-box element on the CmWRKY15-like promoter and inhibited its expression. Additionally, we observed that CmWRKY15-like silencing in chrysanthemum reduced its resistance to F. oxysporum via transgenic experiments. In conclusion, we revealed the mechanism underlying the CmWRKY6-1-CmWRKY15-like cascade response to F. oxysporum infection in chrysanthemum and demonstrated that CmWRKY6-1 and CmWRKY15-like regulates the immune system.
ABSTRACT
Chrysanthemum Fusarium wilt, caused by the pathogenic fungus Fusarium oxysporum, severely reduces ornamental quality and yields. WRKY transcription factors are extensively involved in regulating disease resistance pathways in a variety of plants; however, it is unclear how members of this family regulate the defense against Fusarium wilt in chrysanthemums. In this study, we characterized the WRKY family gene CmWRKY8-1 from the chrysanthemum cultivar 'Jinba', which is localized to the nucleus and has no transcriptional activity. We obtained CmWRKY8-1 transgenic chrysanthemum lines overexpressing the CmWRKY8-1-VP64 fusion protein that showed less resistance to F. oxysporum. Compared to Wild Type (WT) lines, CmWRKY8-1 transgenic lines had lower endogenous salicylic acid (SA) content and expressed levels of SA-related genes. RNA-Seq analysis of the WT and CmWRKY8-1-VP64 transgenic lines revealed some differentially expressed genes (DEGs) involved in the SA signaling pathway, such as PAL, AIM1, NPR1, and EDS1. Based on Gene Ontology (GO) enrichment analysis, the SA-associated pathways were enriched. Our results showed that CmWRKY8-1-VP64 transgenic lines reduced the resistance to F. oxysporum by regulating the expression of genes related to the SA signaling pathway. This study demonstrated the role of CmWRKY8-1 in response to F. oxysporum, which provides a basis for revealing the molecular regulatory mechanism of the WRKY response to F. oxysporum infestation in chrysanthemum.
Subject(s)
Chrysanthemum , Fusarium , Chrysanthemum/metabolism , Fusarium/physiology , Salicylic Acid/metabolism , Signal Transduction/genetics , Plant Diseases/microbiology , Gene Expression Regulation, PlantABSTRACT
BACKGROUND: Fusarium wilt, caused by Fusarium oxysporum f. sp. cucumerinum (Foc), is a severe disease affecting cucumber (Cucumis sativus L.) production worldwide, but mechanisms underlying Fusarium wilt resistance in cucumber remain unknown. To better understand of the defense mechanisms elicited in response to Foc inoculation, RNA sequencing-based transcriptomic profiling of responses of the Fusarium wilt-resistant cucumber line 'Rijiecheng' at 0, 24, 48, 96, and 192 h after Foc inoculation was performed. RESULTS: We identified 4116 genes that were differentially expressed between 0 h and other time points after inoculation. All ethylene-related and pathogenesis-related genes from the differentially expressed genes were filtered out. Real-time PCR analysis showed that ethylene-related genes were induced in response to Foc infection. Importantly, after Foc infection and exogenous application of ethephon, a donor of ethylene, the ethylene-related genes were highly expressed. In response to exogenous ethephon treatment in conjunction with Foc inoculation, the infection resistance of cucumber seedlings was enhanced and endogenous ethylene biosynthesis increased dramatically. CONCLUSION: Collectively, ethylene signaling pathways play a positive role in regulating the defense response of cucumber to Foc infection. The results provide insight into the cucumber Fusarium wilt defense mechanisms and provide valuable information for breeding new cucumber cultivars with enhanced Fusarium wilt tolerance.
