A natural defense: How tea plants use CsALMT6 to fight fluoride toxicity
image: A proposed model for CsALMT6 in response to F stress in tea plants.
Credit: Horticulture Research
Excessive fluoride accumulation in tea leaves poses a potential threat to consumer health. In this study, researchers identified an aluminum-activated malate transporter gene, CsALMT6, that plays a pivotal role in reducing fluoride accumulation and enhancing tolerance in tea plants. Functional analyses revealed that CsALMT6 is highly expressed in older leaves and strongly induced under fluoride stress. Transgenic yeast, Arabidopsis, and Populus overexpressing CsALMT6 showed improved fluoride tolerance, while silencing the gene increased fluoride content in tea plants. The discovery of CsALMT6 provides new insights into the molecular mechanisms of fluoride detoxification and offers a promising genetic target for breeding low-fluoride tea cultivars.
Fluoride, while beneficial in small amounts, can cause health issues such as dental and skeletal fluorosis when consumed excessively. Tea plants (Camellia sinensis), known as fluoride hyperaccumulators, often absorb high levels of fluoride from the soil, particularly in mature leaves, leading to elevated fluoride in tea infusions. Previous studies have identified several transporter genes that regulate fluoride efflux in plants, but the mechanisms underlying fluoride detoxification in tea remain poorly understood. Camellia sinensis appears to possess unique tolerance strategies that allow it to survive under fluoride-rich conditions. Due to these challenges, it is essential to explore new genes and pathways involved in fluoride transport and resistance in tea plants.
A research team from Huazhong Agricultural University has identified a novel gene that helps tea plants cope with fluoride toxicity. The study (DOI: 10.1093/hr/uhae353), published on December 12, 2024, in Horticulture Research, reveals that the aluminum-activated malate transporter CsALMT6 contributes to fluoride resistance in Camellia sinensis by exporting excess fluoride ions from plant cells. Through transcriptome-wide association analysis and transgenic experiments in yeast, Arabidopsis, and Populus, the researchers confirmed that CsALMT6 functions as a key regulator of fluoride detoxification in tea, offering genetic insights for breeding safer tea varieties.
The researchers conducted a transcriptome-wide association study using 203 tea germplasm resources to identify genes linked to fluoride content variation. Among the 16 members of the ALMT gene family, CsALMT6 was singled out as a promising candidate. Expression analysis showed that CsALMT6 was abundant in old leaves and significantly upregulated under fluoride stress. Functional assays revealed that CsALMT6-overexpressing yeast and plants exhibited higher fluoride tolerance, maintaining better growth and lower fluoride accumulation than controls. In Arabidopsis and Populus, CsALMT6 localized to the plasma membrane, suggesting a role in exporting toxic fluoride ions. Conversely, silencing CsALMT6 in tea increased fluoride content, while a compensatory rise in CsALMT9 expression hinted at a possible backup detoxification route. Notably, CsALMT6 expression was markedly stronger in the low-fluoride tea cultivar 'Fuyun 6' than in the high-fluoride cultivar 'Taicha 12', implying a genetic basis for fluoride variation among tea varieties. Collectively, the findings identify CsALMT6 as a central player in maintaining fluoride homeostasis and enhancing plant resistance.
“Tea plants have long fascinated scientists for their remarkable tolerance to fluoride,” said Professor Mingle Wang, corresponding author of the study. “Our discovery of CsALMT6 reveals a new layer of the plant's defense mechanism, showing that this transporter gene helps pump out excess fluoride from cells. This finding not only deepens our understanding of how tea plants adapt to challenging environments but also opens possibilities for developing tea cultivars with safer fluoride levels for consumers worldwide.”
The identification of CsALMT6 offers a promising molecular target for reducing fluoride accumulation in tea, paving the way toward safer and healthier tea production. By integrating CsALMT6 into molecular breeding programs, researchers could develop new cultivars capable of restricting fluoride uptake without compromising growth or quality. Beyond tea, these findings enhance our understanding of fluoride detoxification in plants and may inspire similar genetic interventions in other crops grown in fluoride-enriched soils. Ultimately, the study provides a genetic foundation for achieving both agricultural sustainability and food safety in the global tea industry.
###
References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae353
Funding information
This research was supported by the National Natural Science Foundation of China (32272765 and 31972463), the Natural Science Foundation of Hubei Province (2023AFB877) and the Knowledge Innovation Program of Wuhan-Shuguang Project (2023020201020348).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.