Identificaton of the HAK/KUP/KT Potassium Transporter Gene Family and Functional Analysis of IbHAK5A in Sweet Potato

Potassium (K+) is an essential mineral element for plant growth and development. Members of the HAK/KUP/KT (HAK) gene family play key roles in K+ uptake and ho-meostasis. Although many of them have been extensively identified in a variety of plant species, sweet potato has not yet undergone systemic characterization. In this work, 22 potential IbHAK genes are identified based on phylogenetic analysis, and categorized into four groups (I-IV). We performed comprehensive analysis of IbHAK genes, including protein property, chromosome localization, gene structure, collinear-ity and promoter cis-element investigations for each one. Five IbHAK5 proteins (IbHAK5A-IbHAK5E) were found on the same branch as AtHAK5, OsHAK5, and ZmHAK5, suggesting that small-scale duplication events contributed to the expansion of IbHAK5s in sweet potato. IbHAK5A, a gene highly expressed in various tissues and significantly induced under low-K+ (LK) stress, was cloned and functionally charac-terized in potassium transporter deficient yeast and transgenic Arabidopsis. An AP2/EREBP family transcription factor, IbPTL1, was subsequent identified as having the ability to bind the IbHAK5A promoter and playing a role in regulating the K+ sig-naling pathway. This study provides a foundation for further functional characteriza-tion of HAK/KUP /KT transporters in sweet potato and key candidate genes for further functional analysis, which may be useful for breeding sweet potato that utilizes potas-sium more efficiently in the future.