MYB77 regulates high-affinity potassium uptake by promoting expression of HAK5.

In Arabidopsis, the high-affinity K+ transporter HAK5 is the major pathway for root K+ uptake when below 100 µM; HAK5 responds to Low-K+ (LK) stress by strongly and rapidly increasing its expression during K+ -deficiency. Therefore, positive regulators of HAK5 expression have the potential to improve K+ uptake under LK. Here, we show that mutants of the transcription factor MYB77 share a LK-induced leaf chlorosis phenotype, lower K+ content, and lower Rb+ uptake of the hak5 mutant, but not the shorter root growth, and that overexpression of MYB77 enhanced K+ uptake and improved tolerance to LK stress. Furthermore, we demonstrated that MYB77 positively regulates the expression of HAK5, by binding to the HAK5 promoter and enhances high-affinity K+ uptake of roots. As such, our results reveal a novel pathway for enhancing HAK5 expression under LK stress, and provides a candidate for increasing the tolerance of plants to LK.