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Abstract Under low-potassium (K⁺) stress, a Ca²⁺signaling network consisting of calcineurin B-like proteins (CBLs) and CBL-interacting kinases (CIPKs) play essential roles. Specifically, the plasma membrane CBL1/9-CIPK pathway and the tonoplast CBL2/3-CIPK pathway promotes K⁺uptake and remobilization, respectively, by activating a series of K⁺channels. While the dual CBL-CIPK pathways enable plants to cope with low-K⁺stress, little is known about the early events that link external K⁺levels to the CBL-CIPK proteins. Here we show that K⁺status regulates the protein abundance and phosphorylation of the CBL-CIPK-channel modules. Further analysis revealed low K⁺-induced activation of VM-CBL2/3 happened earlier and was required for full activation of PM-CBL1/9 pathway. Moreover, we identified CIPK9/23 kinases to be responsible for phosphorylation of CBL1/9/2/3 in plant response to low-K⁺stress and the HAB1/ABI1/ABI2/PP2CA phosphatases to be responsible for CBL2/3-CIPK9 dephosphorylation upon K⁺-repletion. Further genetic analysis showed that HAB1/ABI1/ABI2/PP2CA phosphatases are negative regulators for plant growth under low-K⁺, countering the CBL-CIPK network in plant response and adaptation to low-K⁺stress. 

Potassium (K) is an essential macronutrient for plant growth, and its availability in the soil varies widely, requiring plants to respond and adapt to the changing K nutrient status. We show here that plant growth rate is closely correlated with K status in the medium, and this K-dependent growth is mediated by the highly conserved nutrient sensor, target of rapamycin (TOR). Further study connected the TOR complex (TORC) pathway with a low-K response signaling network consisting of calcineurin B-like proteins (CBL) and CBL-interacting kinases (CIPK). Under high K conditions, TORC is rapidly activated and shut down the CBL–CIPK low-K response pathway through regulatory-associated protein of TOR (RAPTOR)–CIPK interaction. In contrast, low-K status activates CBL–CIPK modules that in turn inhibit TORC by phosphorylating RAPTOR, leading to dissociation and thus inactivation of the TORC. The reciprocal regulation of the TORC and CBL–CIPK modules orchestrates plant response and adaptation to K nutrient status in the environment. 

Highly doped semiconductor “designer metals” have been shown to serve as high-quality plasmonic materials across much of the long-wavelength portion of the mid-infrared. These plasmonic materials benefit from a technologically mature semiconductor fabrication infrastructure and the potential for monolithic integration with electronic and photonic devices. However, accessing the short-wavelength side of the mid-infrared is a challenge for these designer metals. In this work we study the perspectives for extending the plasmonic response of doped semiconductors to shorter wavelengths by leveraging charge confinement, in addition to doping. We demonstrate, theoretically and experimentally, negative permittivity across the technologically vital mid-wave infrared (3–5  $\mathrm{\mu <\#comment/>}$m) frequency range. The semiconductor composites presented in our work offer an ideal material platform for monolithic integration with a variety of semiconductor optoelectronic devices operating in the mid-wave infrared. 

We report the theoretical prediction and experimental realization of the optical phenomenon of “ballistic resonance.” This resonance, resulting from the interplay between free charge motion in confining geometries and periodic driving electromagnetic fields, can be utilized to achieve negative permittivity at frequencies well above the bulk plasma frequency. As a proof of principle, we demonstrate all-semiconductor hyperbolic metamaterials operating at frequencies 60% above the plasma frequency of the constituent doped semiconductor “metallic” layer. Ballistic resonance will therefore enable the realization and deployment of various applications that rely on local field enhancement and emission modulation, typically associated with plasmonic materials, in new materials platforms. 

Abstract Efficient optical coupling between nano‐ and macroscale areas is strongly suppressed by the diffraction limit. This work presents a possible solution to this fundamental problem via the experimental fabrication, characterization, and comprehensive theoretical analysis of structures referred to as “photonic funnels.” The funnels represent a novel composite material platform that combines hyperbolic dielectric response with geometry‐assisted optical confinement. Experimentally, funneling of mid‐infrared light through openings with diameters as small as 1/25th of the free space wavelength (λ₀) is demonstrated. By analyzing the optical response of the funnels, as fabricated, both confinement of mid‐infrared radiation to the λ₀/25 areas and efficient outcoupling of light from deep subwavelength areas are confirmed.