Crucial Role of Aluminium-Regulated Flavonol Glycosides (F2-Type) Biosynthesis in Lateral Root Formation of Camellia sinensis.

In acidic soil conditions, aluminium (Al) limits crop growth and yields but benefits the growth of tea plants. Flavonols are suggested to form complexes with Al, enhancing Al accumulation in tea plants. The role of flavonols in promoting lateral root formation under Al stress remains unclear. Here, we identified a 7-rhamnosylated type of flavonol glycosides (F2-type) crucial for this process in tea roots. Al treatment significantly stimulated lateral root initiation and bud germination in tea plants, enhancing flavonol glycoside accumulation, particularly the F2-type. Most genes in the flavonol biosynthetic pathway were upregulated post-Al treatment, including CsUGT89AC2/3 genes, which catalyze F2-type flavonol glycosides synthesis in vitro and in vivo. Overexpression of CsUGT89AC2/3 increased lateral root occurrence, flavonol glycoside accumulation and expression of biosynthetic pathway genes in tea roots. Kaempferol treatment activated flavonol pathway genes and stimulated lateral root growth. Al treatment, kaempferol treatment and CsUGT89AC3 overexpression accelerated auxin accumulation and expression of auxin-related genes. Therefore, Al stimulates flavonol biosynthetic pathway gene expression, regulates F2-type flavonol biosynthesis, and influences auxin homoeostasis, promoting lateral root formation in tea plants. These findings lay the foundation for further investigation into the mechanisms underlying the Al-mediated promotion of lateral root initiation in tea plants.