How DELLAs contribute to control potassium uptake under conditions of potassium scarcity? Hypotheses and uncertainties.

Maintenance of the inward transport of potassium (K) by roots is a critical step to ensure K-nutrition for all plant tissues. When plants are grown at low external K concentrations a strong enhancement of the activity of the AtHAK5 transporter takes place. In a recent work, we observed that the gai-1 mutant of Arabidopsis thaliana, which bears an altered function version of a DELLA regulatory protein, displays reduced accumulation of AtHAK5 transcripts and reduced uptake of Rubidium, an analog for K. In this Addendum we discuss some hypotheses and uncertainties regarding how DELLAs could contribute to the control of K uptake under those conditions. We advance the idea that, following K-restriction, there is a zone and tissue specific regulation of DELLAs by gibberellins through a pathway that likely involves ethylene. According to this model in the epidermis of non-apical zones, DELLAs repress transcription factors that promote AtHAK5 accumulation.