Ectopic Expression of the K Channel β Subunits from Puccinellia tenuiflora ( KPutB1) and Rice ( KOB1) Alters K Homeostasis of Yeast and Arabidopsis.

In this study, we cloned a cDNA for the K channel β subunit from the halophyte Puccinellia tenuiflora and named it KPutB1. KPutB1 was preferentially expressed in the roots and was transiently induced by K-starvation, salt stress, or the combination of both stresses. By yeast two-hybrid assay, we demonstrated that KPutB1 interacts with PutAKT1, α subunit of an AKT1-type K channel of P. tenuiflora. The functional relevance of this interaction on K-nutrition was investigated by co-expression experiments in yeast under various ionic conditions, and K channel α and β subunit homologues from rice ( OsAKT1 and KOB1, respectively) were included for comparison. Yeast co-expressing PutAKT1 and the β subunits ( KPutB1 and KOB1) had better growth and higher K-uptake ability than yeast expressing PutAKT1 alone. In contrast, yeast co-expressing the β subunits ( KPutB1 and KOB1) with OsAKT1 had slower growth and lower K uptake than yeast expressing OsAKT1 alone. Arabidopsis plants over-expressing the K channel β subunit of P. tenuiflora or rice showed increased shoot K content and decreased root Na content under control, 75 mM NaCl, and K-starvation stress conditions. These results suggest that ectopic expression of the K channel β subunit could alter K and Na homeostasis in plants. [ABSTRACT FROM AUTHOR]