Plants are constantly exposed to threats from pathogenic microbes and thus developed an innate immune system to protect themselves. On the other hand, many plants also have the ability to establish endosymbiosis with beneficial microbes such as arbuscular mycorrhizal (AM) fungi or rhizobial bacteria, which improves the growth of host plants. How plants evolved these systems managing such opposite plant-microbe interactions is unclear. We show here that knockout (KO) mutants of OsCERK1, a rice receptor kinase essential for chitin signaling, were impaired not only for chitin-triggered defense responses but also for AM symbiosis, indicating the bifunctionality of OsCERK1 in defense and symbiosis. On the other hand, a KO mutant of OsCEBiP, which forms a receptor complex with OsCERK1 and is essential for chitin-triggered immunity, established mycorrhizal symbiosis normally. Therefore, OsCERK1 but not chitin-triggered immunity is required for AM symbiosis. Furthermore, experiments with chimeric receptors showed that the kinase domains of OsCERK1 and homologs from non-leguminous, mycorrhizal plants could trigger nodulation signaling in legume-rhizobium interactions as the kinase domain of Nod factor receptor1 (NFR1), which is essential for triggering the nodulation program in leguminous plants, did. Because leguminous plants are believed to have developed the rhizobial symbiosis on the basis of AM symbiosis, our results suggest that the symbiotic function of ancestral CERK1 in AM symbiosis enabled the molecular evolution to leguminous NFR1 and resulted in the establishment of legume-rhizobia symbiosis. These results also suggest that OsCERK1 and homologs serve as a molecular switch that activates defense or symbiotic responses depending on the infecting microbes.
The structures of the discotic liquid crystalline (LC) phase of metal-free octa-substituted phthalocyanine (Pc) derivatives were investigated using molecular dynamics (MD) simulations. Special attention was paid to the LC phase structure of the non-peripheral octa-hexyl substituted Pc-derivatives that were recently found to show very high carrier mobilities for the discotic LCs. We obtained spontaneous transition to the columnar hexagonal (Col_{h}) LC phase in a melting simulation from the crystal structure obtained using an x-ray diffraction study. In this simulated Col_{h} structure, the Pc-core normal vectors were tilted 47{∘} from the column axis in parallel within each column, but the tilting directions are disordered between columns. We also found that the inter-core distance was not as large as previously suggested (0.4-0.5 nm) but similar to the common value (0.36 nm). This may resolve the contradiction between the high carrier mobility of the non-peripheral substituted Pcs, because larger inter-core separations degrade the mobilities.
The carrier transport properties
of nonperipheral octahexyl substituted
phthalocyanine H2Pc(C6H13)8
np in its crystal
and columnar (Col) liquid crystal (LC) phase were investigated using
density functional theory (DFT) calculations in combination with molecular
dynamics (MD) and kinetic Monte Carlo (KMC) simulations. In the crystal
phase, we found that the nonperipherally substituted chains of H2Pc(C6H13)8
np, that interpenetrate adjacent phthalocyanines
(Pcs), significantly alter the Pc-core stacking such that higher hole
mobilities are observed for this system than for the nonsubstituted
H2Pc. This chain interpenetration was found to be inherited
by the column stacking in the Col phase and hindered the Pc-core in-plane
rotations between adjacent Pcs. This rotational hindrance further
caused a nonuniform distribution of the adjacent dimer Pc-core in-plane
orientation configurations. The relatively high carrier mobility in
the Col phase in this system can be rationalized by the nonuniform
distribution of the dimer configurations that give relatively high
electronic coupling between the adjacent dimers. Our results show
the remarkable effects of nonperipheral substitutions on the carrier
transport properties in both the crystal and Col LC phases.
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