Root Response to K⁺-Deprivation in Wheat (<i>Triticum aestivum</i> L.): Coordinated Roles of HAK Transporters, AKT2 and SKOR K⁺-Channels, and Phytohormone Regulation

Potassium cation (K⁺) is essential for wheat (<i>Triticum aestivum</i> L.) growth, but the regulatory mechanisms of root response to K⁺ deficiency are not well understood. This study examines how varying durations of K⁺-deprivation affect root K⁺ transport and homeostasis in two wheat varieties, XN979 and YM68. Field pot experiments over three growing seasons showed that XN979 has significantly higher K uptake and productive efficiency than YM68 at a K fertilizer application rate of 60 kg hm⁻². Hydroponic experiments revealed that XN979 has a lower K_m (K⁺ concentrations at which 1/2 of V_max) and a higher V_max (maximum rate of K⁺ uptake) in K⁺ uptake kinetics, indicating better adaptation to K⁺-deficient environments. RNA-seq analysis after different durations of K⁺ deficiency (0, 6, 12, 24, 48 h) showed that genes encoding the Arabidopsis K⁺ Transporter 1 (AKT1) K⁺-channel in both varieties were not significantly upregulated. Instead, K⁺ transport in root primarily depended on high-affinity K⁺ (HAK) transporters. Genes encoding the Arabidopsis K⁺ Transporter 2 (AKT2) K⁺-channel in phloem cells were significantly upregulated under K⁺-deprivation. <i>KOR1</i> and <i>KOR2</i>, encoding the Stelar K⁺ Outward Rectifier (SKOR) K⁺-channel in xylem cells, were significantly downregulated after 6 h and 12 h of K⁺-deprivation, respectively. Significant changes in the expression levels of the Calcineurin B-Like protein–CBL-Interacting Protein Kinase (CBL-CIPK) signaling system and phytohormones synthesis-related genes suggest their involvement in the root response to K⁺-deprivation. These findings clarify the regulation of wheat root responses to K deficiency.