Phenylphenalenone-type phytoalexins in banana (Musa species): a comprehensive review for new research directions

Bananas are the most produced and exported fresh fruit globally; but their sustainable production is always under threat owing to their vegetative reproduction method, in which plants are generated with nearly identical genetic compositions, making them vulnerable to multiple pathogens. To counteract such pathogens, bananas produce phenylphenalenones (PPs) as phytoalexins. PPs are cyclic diarylheptanoids with a tricyclic phenalene-1H-one nucleus attached to a phenyl ring that is produced specifically against multiple pathogens and insect pests in bananas. Since there are no comprehensive studies on banana PPs, the aim of this review was to provide a complete and exhaustive summary with multifaceted biological insights on them. The review begins with a brief description of the significance of banana production, the importance of PPs in banana improvement, and the general background of PPs. Further, we emphasize on the identification of PPs in different banana cultivars against various pathogens, elicitors, and tissues, followed by the antimicrobial activities of PPs against phytopathogens, PPs associated with human health promotion, and the putative biosynthesis pathway of PPs in bananas. PPs could be a potential target for improving the natural defense systems of bananas against multiple pathogens; however, the genes of the underlying biosynthesis pathway remain elusive. We therefore believe that this review will be insightful and potentially assist future studies to discover the genes contributing to PP biosynthesis in bananas and explore their applications in various fields.