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

Potassium cation (K + ) is essential for wheat ( Triticum aestivum 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. KOR1 and KOR2 , 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.