HAK/KUP/KT family potassium transporter genes are involved in potassium deficiency and stress responses in tea plants (Camellia sinensisL.): expression and functional analysis

Background Tea plant is one of the most important non-alcoholic beverage crops worldwide. While potassium (K+) is an essential macronutrient and greatly affects the growth and development of plants, the molecular mechanism underlying K(+)uptake and transport in tea plant root, especially under limited-K(+)conditions, is still poorly understood. In plants, HAK/KUP/KT family members play a crucial role in K(+)acquisition and translocation, growth and development, and response to stresses. Nevertheless, the biological functions of these genes in tea plant are still in mystery, especially their roles in K(+)uptake and stress responses. Results In this study, a total of 21 non-redundantHAK/KUP/KTgenes (designated asCsHAKs) were identified in tea plant. Phylogenetic and structural analysis classified theCsHAKsinto four clusters (I, II, III, IV), containing 4, 8, 4 and 5 genes, respectively. Three major categories ofcis-acting elements were found in the promoter regions ofCsHAKs. Tissue-specific expression analysis indicated extremely low expression levels in various tissues of cluster ICsHAKswith the exception of a high root expression ofCsHAK4andCsHAK5, a constitutive expression of clusters II and IIICsHAKs, and a moderate cluster IVCsHAKsexpression. Remarkably, the transcript levels ofCsHAKsin roots were significantly induced or suppressed after exposure to K(+)deficiency, salt and drought stresses, and phytohormones treatments. Also notably,CsHAK7was highly expressed in all tissues and was further induced under various stress conditions. Therefore, functional characterization ofCsHAK7was performed, and the results demostrated that CsHAK7 locates on plasma membrane and plays a key role in K(+)transport in yeast. Taken together, the results provide promising candidateCsHAKsfor further functional studies and contribute to the molecular breeding for new tea plants varieties with highly efficient utilization of K+. Conclusion This study demonstrated the first genome-wide analysis ofCsHAKfamily genes of tea plant and provides a foundation for understanding the classification and functions of the CsHAKs in tea plants.