Flavonoid-mediated bacterial spermidine biosynthesis enhances vitamin accumulation in tomato fruits

Rhizosphere microbes benefit plant growth and health. How plant-microbe interactions regulate fruit quality remains poorly understood. Here, we elucidate the multi-level modulation of vitamin accumulation in tomato by flavonoid-mediated crosstalk between host plants and rhizosphere microbes. SlMYB12-overexpressing plants with up-regulated flavonoid biosynthesis accumulate higher levels of vitamins C and B₆ in fruits compared to wild-type plants grown in natural soil. Flavonoid-mediated improvement of fruit quality depends on the presence of soil microbiomes and relates to rhizosphere enrichment of key taxa (e.g. Lysobacter). Multi-omics analyses reveal that flavonoids attract Lysobacter soli by stimulating its twitching motility and spermidine biosynthesis, which in turn boosts vitamin accumulation in fruits across tomato cultivars and soil types. RpoN acts as a dual regulator in L. soli that is responsive to flavonoids, controlling bacterial motility and spermidine production. Our study provides insight into flavonoid-mediated rhizosphere signalling and underscores plant-microbiome orchestration for improved tomato fruit quality.