Essential role of the CD docking motif of MPK4 in plant immunity, growth, and development.

MAPKs are universal eukaryotic signaling factors whose functioning is assumed to depend on the recognition of a common docking motif (CD) by its activators, substrates, and inactivators. We studied the role of the CD domain of Arabidopsis MPK4 by performing interaction studies and determining the ligand-bound MPK4 crystal structure. We revealed that the CD domain of MPK4 is essential for interaction and activation by its upstream MAPKKs MKK1, MKK2, and MKK6. Cys181 in the CD site of MPK4 was shown to become sulfenylated in response to reactive oxygen species in vitro. To test the function of C181 in vivo, we generated wild-type (WT) MPK4-C181, nonsulfenylatable MPK4-C181S, and potentially sulfenylation mimicking MPK4-C181D lines in the mpk4 knockout background. We analyzed the phenotypes in growth, development, and stress responses, revealing that MPK4-C181S has WT activity and complements the mpk4 phenotype. By contrast, MPK4-C181D cannot be activated by upstream MAPKK and cannot complement the phenotypes of mpk4. Our findings show that the CD motif is essential and is required for activation by upstream MAPKK for MPK4 function. Furthermore, growth, development, or immunity functions require upstream activation of the MPK4 protein kinase.

Self-Assembled Metal-Organic Complexes for Thermally Reversible Permeabilization of Cell Membranes.

Natural and synthetic membrane active molecules increase the permeability of cell membranes. This can help cells combat multidrug efflux pumps as well as improve signaling and transfection. In this work, thermoresponsive metal-organic complexes (MOCs) have been constructed to transport cell impermeable cargo across the membrane through a pore-aiding assembly. These MOCs can be reversibly controlled as they collapse when the temperature is increased and are simultaneously regenerated when the system is cooled down to room temperature. These ON/OFF molecular valves can be potentially used to overcome multidrug resistance (MDR) in cancer cells and as building blocks for artificial cells.