The Transcription Factor MYB59 Regulates K+/NO3- Translocation in the Arabidopsis Response to Low K+ Stress.

Potassium and nitrogen are essential nutrients for plant growth and development. Plants can sense K+/NO3- levels in soils, and accordingly they adjust root-to-shoot K+/NO3- transport to balance the distribution of these ions between roots and shoots. In this study, we show that the transcription factor MYB59 maintains this balance by regulating the transcription of the Arabidopsis transporter NRT1.5/NPF7.3 in response to low K+ (LK) stress. The myb59 mutant showed a yellow-shoot sensitive phenotype when grown on LK medium. Both the transcript and protein levels of NPF7.3 were remarkably reduced in the myb59 mutant. LK stress repressed transcript levels of both MYB59 and NPF7.3. The npf7.3 and myb59 mutants, as well as the npf7.3 myb59 double mutant, showed similar LK-sensitive phenotypes. Ion content analyses indicated that root-to-shoot K+/NO3- transport was significantly reduced in these mutants under LK conditions. Moreover, ChIP and EMSA assays confirmed that MYB59 bound directly to the NPF7.3 promoter. Expression of NPF7.3 in root vasculature driven by the PHO1 promoter rescued the sensitive phenotype of both npf7.3 and myb59 mutants. Together, these data demonstrate that MYB59 responds to LK stress and directs root-to-shoot K+/NO3- transport by regulating the expression of NPF7.3 in Arabidopsis roots.