Aluminum facilitates flavonol accumulation to modulate sensitivity thresholds of tea roots to aluminum

Abstract

Our previous investigation has reported tea plants are tolerant to aluminum (Al) via a chelation with flavonols. However, the mechanisms by which Al induces flavonol accumulation and modulates the growth of tea plants remain unclear. In this study, we used overexpression, knockout and complementation techniques to target genes in the flavonol biosynthesis pathway to elucidate the physiological responses of plants to Al. In both tea plants and Arabidopsis thaliana, low concentrations Al and kaempferol promoted the root growth, while high concentrations inhibited. As the concentration of Al increased, the accumulation of both Al and flavonols in the root tips of tea plants and A. thaliana increased significantly. Histochemical profiling revealed partially overlapping flavonol- and Al-accumulation sites. RNA-seq results showed that Al enhanced the gene expression of flavonol biosynthetic pathway. Overexpression of the flavonol glycosylation gene CsUGT84J2 significantly promoted the growth of tea roots and enhanced the accumulation of both Al and flavonols. For various Arabidopsis genotypes, at low Al concentrations, greater flavonol accumulation was correlated with enhanced root elongation. Conversely, at high Al concentrations, root elongation was more significantly inhibited, despite increased flavonol accumulation. Therefore, in both tea plants and Arabidopsis, Al promoted root growth at low concentrations and inhibited at high concentrations. Furthermore, Al facilitated flavonol accumulation, and through flavonol-mediated modulation, modify plant responses to Al. These findings contribute to a better understanding of the mechanisms by which Al promotes root growth and provide a scientific basis for the cultivation and management of tea plants.