Verticillium dahliae chromatin remodeling facilitates the DNA damage repair in response to plant ROS stress.

Reactive oxygen species (ROS) production is one of the earliest responses when plants percept pathogens and acts as antimicrobials to block pathogen entry. However, whether and how pathogens tolerate ROS stress remains elusive. Here, we report the chromatin remodeling in Verticillium dahliae, a soil-borne pathogenic fungus that causes vascular wilts of a wide range of plants, facilitates the DNA damage repair in response to plant ROS stress. We identified VdDpb4, encoding a histone-fold protein of the ISW2 chromatin remodeling complex in V. dahliae, is a virulence gene. The reduced virulence in wild type Arabidopsis plants arising from VdDpb4 deletion was impaired in the rbohd mutant plants that did not produce ROS. Further characterization of VdDpb4 and its interacting protein, VdIsw2, an ATP-dependent chromatin-remodeling factor, we show that while the depletion of VdIsw2 led to the decondensing of chromatin, the depletion of VdDpb4 resulted in a more compact chromatin structure and affected the VdIsw2-dependent transcriptional effect on gene expression, including genes involved in DNA damage repair. A knockout mutant of either VdDpb4 or VdIsw2 reduced the efficiency of DNA repair in the presence of DNA-damaging agents and virulence during plant infection. Together, our data demonstrate that VdDpb4 and VdIsw2 play roles in maintaining chromatin structure for positioning nucleosomes and transcription regulation, including genes involved in DNA repair in response to ROS stress during development and plant infection.

Effects of the Superoxide Anionic Radicals to the Cultured Cerebral Cortex Neuron of Newborn Rat.

The effect of the superoxide anionic radicals to the cultured cerebral cortex neuron of newborn rat was investigated by using xanthine oxidase/xanthine. The results are as follows. The growth of neuron was inhibited ATPase activity decreased to 4.223 &mgr;mol/(mg.min(-1))(Pr) total cellular carbonyl increased to 295.40 &mgr;mol/g wet weight lipid peroxides(LPO) increased to 4.87 nmol/g(Pr) membrane lipid fluidity decreased (P value 0.398) in nuclear DNA, thesingle strand breaks(SSB) increased in the single cell gel assay(SCG), DNA migration was 7.35 mm ݣ subcellular structures of the neuron changed (mitochondria were swelling, etc.) and SOD gene expression of the neuron increased (the SOD activity and the SOD content increased, SOD mRNA content increased). These suggest that the superoxide anionic radicals could damage proteins, nucleic acids, lipids and subcellular structures in neurons.

Presynaptic alpha-7 nicotinic acetylcholine receptors modulate excitatory synaptic transmission in hippocampal neurons.

The effects of presynaptic nicotinic acetylcholine receptors (nAChRs) on excitatory synaptic transmission in CA1 pyramidal neurons of the rat hippocampus were examined by blind whole-cell patch clamp recording from hippocampal slice preparations. Local application of the nAChRs agonist dimethylphenyl-piperazinium iodide (DMPP) did not induce a postsynaptic current response in CA1 pyramidal cells. However, DMPP enhanced the frequency and amplitude of spontaneous excitatory postsynaptic current (sEPSC) in these cells in a dose-dependent manner. This enhancement was blocked by the selective nicotinic alpha-7 receptor antagonist alpha-bungarotoxin, but not by the antagonist mecamylamine, hexamethonium or dihydro-beta-erythroidine. The frequency of miniature excitatory postsynaptic current (mEPSC) in CA1 pyramidal neurons was also increased by application of DMPP, indicating a presynaptic site of action of the agonist. Taken together, these results suggest that activation of presynaptic nAChRs in CA1 pyramidal neurons, which contain alpha-7 subunits, potentiates presynaptic glutamate release and consequently modulate excitatory synaptic transmission in the hippocampus.