Aluminum-activated malate transporter family member CsALMT6 mediates fluoride resistance in tea plants (Camellia sinensis)

Tea plant is a fluoride (F)-hyperaccumulator, which poses a potential threat to human health via tea consumption. Reducing F accumulation in fresh tea leaves is crucial for enhancing the safety of tea production at its source. This study aims to isolate novel genes responsible for F accumulation or transport in tea plants. We identified an aluminum (Al)-activated malate transporter gene, CsALMT6, which was hypothesized to be a candidate for differential F accumulation in Camellia sinensis, by employing a combination of transcriptome-wide association study (TWAS) and genome-wide identification of the CsALMT gene family. CsALMT6 exhibited high expression levels in old leaves, and its expression was significantly upregulated in tea plants subjected to F-stress conditions. Furthermore, heterologous expression of CsALMT6 in yeast, Arabidopsis, and Populus conferred F tolerance. However, the expression of F-tolerant hub genes, CsFEX1 and CsFEX2, remained unaffected in CsALMT6-silenced tea plants. Additionally, under F toxicity conditions, the transcription of CsALMT6 was negatively associated with F accumulation in tea plants. In conclusion, CsALMT6 plays a vital role in reducing F accumulation in C. sinensis, thus conferring F tolerance to plant cells.