Molecular mechanisms underlying plant adaptation to low potassium stress

Potassium (K⁺) is an essential macronutrient and the most abundant inorganic cation in plant cells. Efficient acquisition, allocation, and homeostatic maintenance of K⁺ are critical for plant growth, development, and stress tolerance. However, K⁺ availability in soils is often limited and highly variable, necessitating sophisticated adaptive mechanisms to maintain K⁺ homeostasis under Low K⁺ (LK) stress. Over the past decade, substantial progress has been made in dissecting the molecular regulatory networks that govern plant responses to LK stress. Here, we review recent advances in the two central K⁺ uptake systems, the Shaker-type channel Arabidopsis K⁺ Transporter 1 (AKT1) and High-Affinity K⁺ Transporter 5 (HAK5). We further summarize the CBL-CIPK calcium-signaling network as a central hub for decoding LK signals. It operates through sequential activation of a tonoplast-localized CBL2/3-CIPK module and a plasma membrane-localized CBL1/9-CIPK23 module. This temporal ordering is supported by the earlier activation of the tonoplast module, which is itself required for the full activation of the plasma membrane module. We highlight its newly discovered antagonistic crosstalk with the target of rapamycin complex (TORC) growth pathway, which couples K⁺ status to the balance between growth and stress adaptation. We further present an expanding transcriptional regulatory network, with particular attention to the functional roles of newly identified transcription factors in modulating LK responses. We also discuss conserved and distinct regulatory mechanisms characterized in major cereal and economic crops. Together, these post-translational and transcriptional mechanisms clarify how plants sense and adapt to potassium deficiency, and offer theoretical guidance and candidate genetic targets for breeding potassium-efficient crop varieties.