Research progress of endophytes and their secondary metabolites in Morus plants

Morus plants are globally recognized as essential economic woody species. Investigating cross-kingdom interaction mechanisms between Morus and endophytes, along with the regulatory networks of secondary metabolism, is crucial for sustainable agricultural development and innovative drug research. However, systematic analyses remain lacking. The variations in endophytic communities across different mulberry species, varieties, and tissues have not been fully elucidated. This review systematically reviewed the diverse characteristics of endophytes in Morus plants and the biological activities of their secondary metabolites, with particular emphasis on the co-evolution mechanisms between endophytes and their hosts. It was demonstrated that the endophytic communities in Morus plants exhibited significant species-specific differences, tissue specificity, and cultivar dependence. These endophytic communities enhance host nutrient utilization efficiency and promote plant growth through metabolic reciprocity, primarily via nitrogen fixation and phosphorus solubilization. Furthermore, they directly synthesize bioactive metabolites (such as flavonoids and alkaloids) while functioning as biological elicitors that activate host secondary metabolic pathways, thereby facilitating secondary metabolites accumulation. Additionally, endophytes were observed to improve host stress resistance by enhancing photosynthetic efficiency, maintaining ion homeostasis, and regulating soil nutrients. Hairy root cultures facilitate industrial-scale production of secondary metabolites from Morus plants through efficient biosynthesis platforms. This review established a theoretical foundation for in-depth analyses of plant-microbe cross-kingdom interaction networks and the development of targeted regulation technologies. Future research should prioritize investigations into dynamic metabolic interaction mechanisms and ecological safety assessments of engineered strains.