An RNA-Seq transcriptome analysis revealing novel insights into fluorine absorption and transportation in the tea plant

The tea plant [Camellia sinensis (L) O. Kuntze] is a species with a high concentration of fluorine in its leaves, especially in the mature leaves. The physiological mechanisms for fluorine absorption and accumulation have been well studied, but the related molecular mechanisms are poorly understood in the tea plant. In this study, transcriptome analysis by RNA-Seq following exposure to 16 mg/L of fluorine for 0, 3, 6, and 24 h was performed to identify the candidate genes involved in the transmembrane transportation of fluorine. More than 1.23 billion high-quality reads were generated, and 259.84 million unigenes were assembled de novo. with 518 216 of them being annotated in the seven databases used. Meanwhile, a large number of transporters, transcription factors, and heat-shock proteins with differential expression in response to high levels of fluorine (P <= 0.05) were identified. Comparative transcriptome analysis showed that the uptake of fluorine is related to photosynthesis, plant hormone signal transduction, and glutathione metabolism. Further systematic analysis of nitrate and potassium transporter genes revealed that many of these genes regulate fluorine transportation in roots and leaves. Gene expression and fluorine content analysis in different cultivars revealed CsNRT1/PTR 3.1 and CsPT 8 as the key genes regulating the transmembrane transportation of fluorine in the tea plant.