Intraspecific variation in defense against a generalist lepidopteran herbivore in populations of Eruca sativa (Mill.)

Populations of Eruca sativa (Brassicaceae) from desert and Mediterranean (Med) habitats in Israel differ in their defense against larvae of the generalist Spodoptera littoralis but not the specialist Pieris brassicae. Larvae of the generalist insect feeding on plants of the Med population gained significantly less weight than those feeding on the desert plants, and exogenous application of methyl jasmonate (MJ) on leaves of the Med plants significantly reduced the level of damage created by the generalist larvae. However, MJ treatment significantly induced resistance in plants of the desert population, whereas the generalist larvae caused similar damage to MJ‐induced and noninduced plants. Analyses of glucosinolates and expression of genes in their synthesis pathway indicated that defense in plants of the Med population against the generalist insect is governed by the accumulation of glucosinolates. In plants of the desert population, trypsin proteinase inhibitor activity was highly induced in response to herbivory by S. littoralis. Analysis of genes in the defense‐regulating signaling pathways suggested that in response to herbivory, differences between populations in the induced levels of jasmonic acid, ethylene, and salicylic acid mediate the differential defenses against the insect. In addition, expression analysis of myrosinase‐associated protein NSP2 suggested that in plants of the desert population, glucosinolates breakdown products were primarily directed to nitrile production. We suggest that proteinase inhibitors provide an effective defense in the desert plants, in which glucosinolate production is directed to the less toxic nitriles. The ecological role of nitrile production in preventing infestation by specialists is discussed.     

Active mutants of the TCR-mediated p38α alternative activation site show changes in the phosphorylation lip and DEF site formation

The p38α mitogen-activated protein kinase is commonly activated by dual (Thr and Tyr) phosphorylation catalyzed by mitogen-activated protein kinase kinases. However, in T-cells, upon stimulation of the T-cell receptor, p38α is activated via an alternative pathway, involving its phosphorylation by zeta-chain-associated protein kinase 70 on Tyr323, distal from the phosphorylation lip. Tyr323-phosphorylated p38α is autoactivated, resulting in monophosphorylation of Thr180. The conformational changes induced by pTyr323 mediating autoactivation are not known. The lack of pTyr323 p38α for structural studies promoted the search for Tyr323 mutations that may functionally emulate its effect when phosphorylated. Via a comprehensive mutagenesis of Tyr323, we identified mutations that rendered the kinase intrinsically active and others that displayed no activity. Crystallographic studies of selected active (p38α^Y323Q, p38α^Y323T, and p38α^Y323R) and inactive (p38α^Y323F) mutants revealed that substantial changes in interlobe orientation, extended conformation of the activation loop, and formation of substrate docking DEF site (docking site for extracellular signal-regulated kinase FXF) interaction pocket are associated with p38α activation.     

Solving the Capacitive Paradox of 2D MXene using Electrochemical Quartz‐Crystal Admittance and In Situ Electronic Conductance Measurements

Fast ion adsorption processes in supercapacitors enable quick storage/delivery of significant amounts of energy, while ion intercalation in battery materials leads to even larger amounts of energy stored, but at substantially lower rates due to diffusional limitations. Intercalation of ions into the recently discovered 2D Ti₃C₂T_x (MXene) occurs with a very high rate and leads to high capacitance, posing a paradox. Herein, by characterizing the mechanical deformations of MXene electrode materials at various states‐of‐charge with a variety of cations (Li, Na, K, Cs, Mg, Ca, Ba, and three tetra­alkylammonium cations) during cycling by electrochemical quartz‐crystal admittance (EQCA, quartz‐crystal microbalance with dissipation monitoring) combined with in situ electronic conductance and electrochemical impedance, light is shone on this paradox. Based on this work, it appears that the capacitive paradox stems from cationic insertion, accompanied by significant deformation of the MXene particles, that occurs so rapidly so as to resemble 2D ion adsorption at solid‐liquid interfaces. The latter is greatly facilitated by the presence of water molecules between the MXene sheets.     

DEF Pocket in p38α Facilitates Substrate Selectivity and Mediates Autophosphorylation

Signaling processes are primarily promoted by molecular recognition and corresponding protein-protein interactions. One of the key eukaryotic signaling pathways is the MAP kinase cascade involved in vital cellular processes such as cell proliferation, differentiation, apoptosis, and stress response. The principle recognition site of MAP kinases, the common docking (CD) region, forms selective interactions with substrates, upstream activators, and phosphatases. A second docking site, defined as the DEF site interaction pocket (DEF pocket), is formed subsequent to ERK2 and p38α activation. Both crystal structures of p38α in its dually phosphorylated form and of intrinsically active mutants showed the DEF pocket, giving motivation for studying its role in substrate activation and selectivity. Mutating selected DEF pocket residues significantly decreased the phosphorylation levels of three p38α substrates (ATFII, Elk-1, and MBP) with no apparent effect on the phosphorylation of MK2 kinase. Conversely, mutating the CD region gave the opposite effect, suggesting p38α substrates can be classified into DEF-dependent and DEF-independent substrates. In addition, mutating DEF pocket residues decreased the autophosphorylation capability of intrinsically active p38α mutants, suggesting DEF-mediated trans-autophosphorylation in p38α. These results could contribute to understanding substrate selectivity of p38α and serve as a platform for designing p38α-selective DEF site blockers, which partially inhibit p38α binding DEF-dependent substrates, whereas maintaining its other functions intact. In this context, preliminary results using synthetic peptides reveal significant inhibition of substrate phosphorylation by activated p38α.