The Pepper Mitogen-Activated Protein Kinase CaMAPK7 Acts as a Positive Regulator in Response to Ralstonia solanacearum Infection.

Mitogen-activated protein kinase (MAPK) pathways play a vital role in multiple plant processes, including growth, development, and stress signaling, but their involvement in response to Ralstonia solanacearum is poorly understood, particularly in pepper plants. Herein, CaMAPK7 was identified from the pepper genome and functionally analyzed. The accumulations of CaMAPK7 transcripts and promoter activities were both significantly induced in response to R. solanacearum strain FJC100301 infection, and exogenously applied phytohormones, including methyl jasmonate (MeJA), brassinolide (BR), salicylic acid (SA), and ethephon (ETN), were decreased by abscisic acid (ABA) treatment. Virus-induced gene silencing (VIGS) of CaMAPK7 significantly enhanced the susceptibility of pepper plants to infection by R. solanacearum and downregulated the defense-related marker genes, including CaDEF1, CaPO2, CaSAR82A, and CaWRKY40. In contrast, the ectopic overexpression of CaMAPK7 in transgenic tobacco enhanced resistance to R. solanacearum and upregulated the defense-associated marker genes, including NtHSR201, NtHSR203, NtPR4, PR1a/c, NtPR1b, NtCAT1, and NtACC. Furthermore, transient overexpression of CaMAPK7 in pepper leaves triggered intensive hypersensitive response (HR)-like cell death, H2O2 accumulation, and enriched CaWRKY40 at the promoters of its target genes and drove their transcript accumulations, including CaDEF1, CaPO2, and CaSAR82A. Taken together, these data indicate that R. solanacearum infection induced the expression of CaMAPK7, which indirectly modifies the binding of CaWRKY40 to its downstream targets, including CaDEF1, CaPO2, and CaSAR82A, ultimately leading to the activation of pepper immunity against R. solanacearum. The protein that responds to CaMAPK7 in pepper plants should be isolated in the future to build a signaling bridge between CaMAPK7 and CaWRKY40.

Tungsten Carbide Encapsulated in Grape-Like N-Doped Carbon Nanospheres: One-Step Facile Synthesis for Low-Cost and Highly Active Electrocatalysts in Proton Exchange Membrane Water Electrolyzers.

Tungsten carbide (WC) is an alternative to the costly and resource-constrained Pt-based catalysts. Herein, a one-step facile and easily scalable approach is reported to synthesize ultrafine WC nanocrystals encapsulated in porous N-doped carbon nanospheres (NC) by simple self-polymerization, drying, and annealing. It is worth mentioning that this developed method has four novel features: (1) the synthesis process, without any hard template or hydrocarbon gas feeding, is, notably, very facile and efficient with low cost; (2) the carbon coating on WC nanocrystals not only restrains coarsening of particles but also creates strong coupling interactions between the nanocrystallines and the conductive carbonaceous matrix; (3) uniform grape-like WC@NC nanospheres with high specific surface area can be obtained in a large scale; and (4) single-phase WC can be achieved. As a result, WC@NC demonstrates remarkable hydrogen evolution reaction (HER) electrocatalytic performance with overpotentials of 127 and 141 mV at a current density of 10 mA cm-2 and Tafel slopes of 56.3 and 78.7 mV dec-1 in acid and alkaline media, respectively. Our density functional theory calculations manifest that the strong synergistic electronic effect between WC and its intimately bonded carbon shell vastly boosts the HER electrocatalytic activity. WC@NC catalysts as a cathode are further tested in a home-made electrolyzer with 0.78 A cm-2 achieved at a cell voltage of 2 V at 80 °C and operated stably at 200 mA cm-2 for more than 20 h.