Molecular Mechanisms Of ABC Transporter Mediated Transmembrane Absorption And Transport Of Fluoride By Tea Plant Roots

Tea plant is a highly fluoride(F)enriched plant.F is mainly absorbed from soil by root and accumulated in the tea leaves.F can enter into human body through drinking tea liquid.The high level of F in tea leaves seriously threatens tea quality and safety as well as human health.Active absorption of F by root is the main way that F accumulated in tea plants,however,the potential mechanism of the transmembrane absorption and transport of F in tea root remains unclear.ABC transporters can provide energy and transmembrane transport channels for plants in the process of absorbing nutrient elements through transmembrane.It is speculated that ABC transporters may play an important role in mediating the transmembrane absorption and transport of F in tea plant roots.Therefore,it is important to ascertain the mechanism of ABC transporters mediating the transmembrane absorption of F in tea plant roots and regulating the absorption and enrichment of F in tea plant roots.Above results will provide a critical data to ensure the quality and safety of tea leaves.The effect of chloride ion on the absorption and enrichment of F in different tea plant varieties was systematically analyzed in this paper;the impact of F on the content of ABC transporters protein in tea roots as well as the differentially expressed genes of ABC transporters by RNA-Seq technology was also investigated.The expression patterns,bioinformatics and evolution of ABC transporter genes was examined.Results from this paper will provide a theoretical basis for revealing the microscopic mechanism of ABC transporters mediating the absorption and transport of F across the membrane of tea plant roots.The main results are as follows:(1)Different organs of tea plants have different absorption and enrichment laws of F.The F accumulated in tea plant showed the the law of leaf>stem>root before F addition;while it expressed the law of leaf>root>stem after F treatment.(2)Chlorine(Cl-)promoted the absorption of F by "Shu Cha Zao",but it inhibited the absorption of F-by other tea plant varieties,which indicated that the mechanism of chlorine on the absorption and enrichment of F-in different tea plant varieties was quite different.(3)In the transcriptome,a total of 910 genes obtained from the three databases of NR,GO,and KEGG which were annotated as ABC transporters.Of which 51 were DEGs.After F-treatment,the DEGs involved in the roots of tea plants were the most abundant,and the number of DEGs was significantly reduced after the addition of Cl-.(4)GO functional analysis showed that ABC transporters mainly located in the membrane system in the cellular components,and its molecular functions mainly with binding ATP or transport activity.In biological processes,ABC transporters has the function of transmembrane transport,tissue formation,material transport and response.In the KEGG functional analysis,10 pathway branches in the ABC transporter pathway(ko02010)were annotated,including 5 subfamilies such as ABCA,ABCB,ABCC,ABCD,and ABCG.The K05658 pathway has DEGs among the different treatments,and the number of DEGs involved is the largest one.(5)F induced the expression of ABC transporters,which significantly increased their protein content and accelerated ATP hydrolysis to release energy,increased electrochemical potential energy,and induced a large number of F ions entering across the membrane into the cell.(6)The expression level of differentially expressed gene CsCL667 was up-regulated under the induction of F,the transport ability of ABC transporter to F is enhanced,which accelerated a large amount of F entering and accumulating the cell.This result verified that the ABC transporter has the ability to transport F by tea plant F transporter.(7)From genetic function prediction analysis showed that CsCL667 protein contained typical ABC transporter domain and contained 2 transmembrane domain membrane proteins.The phylogenetic tree analysis also showed that CsCL667 proteins in tea plant and CsFEX of the fluorine ion transporters in tea plants on different branches of the same gene family,which indicated that they may have the similar expression patterns or biological functions.(8)By E.coli heterologous system verification,found that the CsCL667 has a certain fluorine resistance and the function of fluorine ion efflux.