Integrated metabolomics and transcriptomics analyses reveal aluminum-activated malate transporter CsALMT14 contributing to fluoride tolerance in F-hyperaccumulator Camellia sinensis

Tea plants (Camellia sinensis) tend to accumulate excessive amounts of fluoride (F) compared to other plants. However, the specific mechanisms of F tolerance or detoxification in tea plants remain insufficiently understood. This study employed ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) to identify critical metabolites involved in F detoxification across two distinct tea plant cultivars with varying F accumulation capacities. Notably, malic acid and citric acid emerged as key metabolites that differentially accumulated under F-stressed conditions. Weighted gene co-expression network analysis indicated that C. sinensis aluminum (Al)-activated malate transporter genes CsALMT9 and CsALMT14 may be implicated in the response to F stress in C. sinensis. Further investigations revealed that CsALMT14 localized to the plasma membrane and exhibited significant transcriptional induction upon exposure to F toxicity. Moreover, heterologous expression of CsALMT14 enhanced F tolerance by mitigating F accumulation in transgenic yeast and Arabidopsis thaliana. Additionally, silencing of CsALMT14 by antisense oligodeoxynucleotide and virus-induced gene silencing reduced the content of malic acid but increased the accumulation of citric acid in tea plants, which might be attributed to the down-regulated expression of malic acid synthesis- and citric acid degradation-related genes. These findings suggest that CsALMT14 confers tolerance to F toxicity through F efflux and regulation of malic acid and citric acid metabolism-related gene expression, thereby providing a novel strategy for F detoxification in tea plants.