Potassium is an essential mineral element for plant growth and development. Although it is known that plants absorb and transport K+ through membrane transporters, it remains unclear how these transporters are regulated. Here we show that the protein kinase CIPK23, encoded by the LKS1 gene, regulates K+ uptake under low-K+ conditions. Lesion of LKS1 significantly reduced K+ uptake and caused leaf chlorosis and growth inhibition, whereas overexpression of LKS1 significantly enhanced K+ uptake and tolerance to low K+. We demonstrate that CIPK23 directly phosphorylates the K+ transporter AKT1 and further find that CIPK23 is activated by the binding of two calcineurin B-like proteins, CBL1 and CBL9. We propose a model in which the CBL1/9-CIPK23 pathway ensures activation of AKT1 and enhanced K+ uptake under low-K+ conditions.

Microfilament dynamics play a critical role in regulating stomatal movement; however, the molecular mechanism underlying this process is not well understood. We report here the identification and characterization of STOMATAL CLOSURE-RELATED ACTIN BINDING PROTEIN1 (SCAB1), an Arabidopsis thaliana actin binding protein. Plants lacking SCAB1 were hypersensitive to drought stress and exhibited reduced abscisic acid-, H 2 O 2 -, and CaCl 2 -regulated stomatal movement. In vitro and in vivo analyses revealed that SCAB1 binds, stabilizes, and bundles actin filaments. SCAB1 shares sequence similarity only with plant proteins and contains a previously undiscovered actin binding domain. During stomatal closure, actin filaments switched from a radial orientation in open stomata to a longitudinal orientation in closed stomata. This switch took longer in scab1 plants than in wild-type plants and was correlated with the delay in stomatal closure seen in scab1 mutants in response to drought stress. Our results suggest that SCAB1 is required for the precise regulation of actin filament reorganization during stomatal closure.

Potassium transporters play crucial roles in K + uptake and translocation in plants. However, so far little is known about the regulatory mechanism of potassium transporters. Here, we show that a Shaker-like potassium channel AtKC1, encoded by the AtLKT1 gene cloned from the Arabidopsis thaliana low-K + (LK)-tolerant mutant Atlkt1, significantly regulates AKT1-mediated K + uptake under LK conditions. Under LK conditions, the Atkc1 mutants maintained their root growth, whereas wild-type plants stopped their root growth. Lesion of AtKC1 significantly enhanced the tolerance of the Atkc1 mutants to LK stress and markedly increased K + uptake and K + accumulation in the Atkc1-mutant roots under LK conditions. Electrophysiological results showed that AtKC1 inhibited the AKT1-mediated inward K + currents and negatively shifted the voltage dependence of AKT1 channels. These results demonstrate that the 'silent' K + channel α-subunit AtKC1 negatively regulates the AKT1-mediated K + uptake in Arabidopsis roots and consequently alters the ratio of root-to-shoot under LK stress conditions. Keywords: Arabidopsis; potassium channel; low-K + stress; AKT1; AtKC1 Cell Research (2010) IntroductionPotassium is an essential mineral element for plant growth and development, and it plays essential roles in many important physiological and biochemical processes in living plant cells, such as regulation of enzyme activation, electrical neutralization, osmoregulation, control of membrane potential, co-transport of sugars, and so on [1,2]. Plant growth and development need millimolar K + in the soil or growth medium, but typical K + concentration at the interface of roots and soils is within micromolar range [3]. Thus, plants often encounter low-K + (LK) stress under natural conditions. Although different plants or different genotypes of a plant species show varied K + utilization efficiency [4], most plants show K + -deficient symptom under LK stress, typically leaf chlorosis and subsequent inhibition of plant growth and development [5].Absorption of K + by plant cells and K + translocation between different tissues and organs in plants are mediated by plant K + transporters and channels [2,6,7]. Over the past decade, a large number of genes encoding plant K + transporters and channels, particularly for Arabidopsis, have been characterized [6][7][8]. These K + transporters vary in K + affinity, kinetics, transcriptional modulation, regulatory mechanism, etc [2,[6][7][8], and they compose a complex system for plant K + uptake and translocation. Among these K + transporters and channels, members of the Shaker K + channel family are well characterized for their potential functions and are probably the most important for K + uptake and transport in Arabidopsis [8] Recent reports showed that channel heterotetramerization is a key regulatory mechanism for K + channels, which was found not only in animals [14][15][16] but also in plants [17,18]. Different kinds of potassium channel subunits may assemble together to form functional heteromer...

As a common neurotransmitter in the nervous system, γ-aminobutyric acid (GABA) modulates locomotory patterns in both vertebrates and invertebrates. However, the signaling mechanisms underlying the behavioral effects of GABAergic modulation are not completely understood. Here, we demonstrate that a GABAergic signal in C. elegans modulates the amplitude of undulatory head bending through extrasynaptic neurotransmission and conserved metabotropic receptors. We show that the GABAergic RME head motor neurons generate undulatory activity patterns that correlate with head bending and the activity of RME causally links with head bending amplitude. The undulatory activity of RME is regulated by a pair of cholinergic head motor neurons SMD, which facilitate head bending, and inhibits SMD to limit head bending. The extrasynaptic neurotransmission between SMD and RME provides a gain control system to set head bending amplitude to a value correlated with optimal efficiency of forward movement.DOI: http://dx.doi.org/10.7554/eLife.14197.001

The development of a polarized neuron relies on the selective transport of proteins to axons and dendrites. Although it is well known that the microtubule cytoskeleton has a central role in establishing neuronal polarity, how its specific organization is established and maintained is poorly understood. Using the in vivo model system Caenorhabditis elegans, we found that the highly conserved UNC-119 protein provides a link between the membrane-associated Ankyrin (UNC-44) and the microtubule-associated CRMP (UNC-33). Together they form a periodic membrane-associated complex that anchors axonal and dendritic microtubule bundles to the cortex. This anchoring is critical to maintain microtubule organization by opposing kinesin-1 powered microtubule sliding. Disturbing this molecular complex alters neuronal polarity and causes strong developmental defects of the nervous system leading to severely paralyzed animals.

It was previously found that soybean protein hydrolysates (SPHs) can bind with calcium to form soluble complexes and promote calcium uptake by Caco-2 cells. However, the role of SPHs-calcium complexes on bone mass still needs to be explored. Fast growing male and female rats (n = 72) were assigned to eight groups: Control, lactic acid calcium (LCa), SPHs-calcium complexes (SPHCa) and casein phosphopeptides calcium (CPPCa). After four weeks treatment, oral administration of SPHCa significantly increased femur BMD of rats compared with Control and LCa groups (P < 0.05), while there are no obvious difference on the BMD of femur and lumbar vertebrae between SPHCa and CPPCa groups. Also, SPHCa showed a tendency to improve the mechanical properties of vertebra lumber for female rats. These findings suggest that the SPHs-calcium complexes might have positive effects on bone accretion of fast growing animals. This study brings new insight for better understanding the role of soybean protein itself on bone mass.

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