Metabolomic, Biochemical, and Gene Expression Analyses Reveal the Underlying Responses of Resistant and Susceptible Banana Species during Early Infection with Fusarium oxysporum f. sp. cubense.

Banana (Musa spp.) is an important staple and economic fruit crop, especially in Africa, Southeast Asia, and Latin America. The wilt disease caused by Fusarium oxysporum f. sp. cubense, especially F. oxysporum f. sp. cubense strain TR4, is disastrous for banana production. Banana plants infected by F. oxysporum f. sp. cubense TR4 gradually die from leaf blight or vascular rot. There is no efficient method to control this disease, and the underlying response of banana plants to F. oxysporum f. sp. cubense remains unknown. In this study, the responses of an economically important banana cultivar, the F. oxysporum f. sp. cubense-susceptible 'BX', and a wild banana relative, the F. oxysporum f. sp. cubense-resistant Musa yunnanensis ('YN'), to F. oxysporum f. sp. cubense infection were investigated using metabolomic, biochemical, and molecular biological methods. Numerous metabolomic compounds, including defense-responsive signaling molecules, phytohormones, phenolics, and antioxidants, were identified through metabolomic analysis. Changes in salicylic acid (SA), methyl-jasmonic acid, abscisic acid (ABA), cytokinin, 3-indoleacetic acid, gibberellic acid, and total phenolic levels were detected using liquid chromatography-mass spectrometry and the Folin-Ciocalteu method. The expression levels of genes involved in the biosynthesis of some defense-responsive compounds were studied through quantitative real-time polymerase chain reaction. The results revealed that the resistant YN had a larger change in SA content and a lower ABA level throughout the early infection period, compared with the levels in BX. The susceptible BX had a lower phenolic content. The resistant YN also expressed pathogenesis-related (PR) genes, especially PR1, PR4, PR5-1, and PDF2.2, at higher levels than the susceptible BX. These dynamic metabolic and gene-expression profiles from susceptible and resistant banana during the early stage of F. oxysporum f. sp. cubense infection increase our understanding of the complex interaction response between this crop and its pathogen.