Functional characterization of GhAKT1, a novel Shaker-like K⁺ channel gene involved in K⁺ uptake from cotton (Gossypium hirsutum)

Abstract

Shaker-like potassium (K(+)) channels in plants play an important role in K(+) absorption and transport. In this study, we characterized a Shaker-like K(+) channel gene GhAKT1 from the roots of Gossypium hirsutum cv. Liaomian17. Phylogenetic analysis showed that the GhAKT1 belongs to the AKT1-subfamily in the Shaker-like K(+) channel family. Confocal imaging of a GhAKT1-green fluorescent fusion protein (GFP) in transgenic Arabidopsis plants indicated that GhAKT1 is localized in the plasma membrane. Transcript analysis located GhAKT1 predominantly in cotton leaves with low abundance in roots, stem and shoot apex. Similarly, β-glucuronidase (GUS) activity was detected in both leaves and roots of PGhAKT1::GUS transgenic Arabidopsis plants. In roots, the GUS signals appeared in the epidermis, cortex and endodermis and root hairs, suggesting the contribution of GhAKT1 to K(+) uptake. In leaves, GhAKT1 was expressed in differentiated leaf primordial as well as mesophyll cells and veins of expanded leaves, pointing to its involvement in cell elongation and K(+) transport and distribution in leaves. Severe K(+) deficiency did not affect the expression of GhAKT1 gene. GhAKT1-overexpression in either the Arabidopsis wild-type or akt1 mutant enhanced the growth of transgenic seedlings under low K(+) deficiency and raised the net K(+) influx in roots at 100μM external K(+) concentration, within the range of operation of the high-affinity K(+) uptake system. The application of 2mM BaCl2 resulted in net K(+) efflux in roots, and eliminated the differences between GhAKT1-overexpression lines and their acceptors indicating that the K(+) uptake mediated by GhAKT1 is also as Ba(2+)-sensitive as AtAKT1.

Keywords: Expression profiles; K(+) uptake; Overexpression; Shaker-like K(+) channel.