Abstract: Apocynum venetum is a typical K⁺-efficient species with notably high K⁺ uptake and utilization efficiency under K⁺-deficiency conditions. Furthermore, A. venetum can maintain high plant tissue K⁺ contents and K⁺/Na⁺ ratio through enhancement of the capacity for selective absorption and transport of K⁺ under salinity or drought conditions. In order to investigate the underlying molecular mechanisms, a potassium channel gene, designated AvAKT1, was isolated from the root of A. venetum using RT-PCR and RACE methodologies. The full cDNA sequence was 2906 bp in length, encoding 899 amino acid residues. The deduced amino acids of AvAKT1 exhibited all the structural features shared by other plant Shaker-like K⁺-channel family members, including six transmembrane helices, a K⁺-selective pore-forming domain, a cyclic nucleotide-binding domain (cNBD), an ankyrin-related domain (ANKY) and a domain rich in hydrophobic and acidic residues (KHA). The phylogenetic analysis showed that AvAKT1 belonged to Group Ⅰ (AKT1-subfamily) in the Shaker-like K⁺ channel family, and formed a clade with the closest relation to the dicotyledon AKT1 homologue NtAKT1 from Nicotiana tabacum. Real-time fluorescent quantitative PCR suggested that AvAKT1 is expressed especially in roots. Furthermore, AvAKT1 was induced strongly by supplying of 5 mmol·L^-1 K⁺ in the medium. The expression level of AvAKT1 was significantly increased within a short time (e.g. 6 h) under -0.2 MPa osmotic stress or 25 mmol·L^-1 NaCl treatment. These results indicate that AvAKT1 is probably involved in the process of low affinity K⁺ absorption, and might play an effective role in response to salinity or drought in A. venetum.

Key words: Apocynum venetum, AvAKT1, K⁺, gene cloning, expression analysis