Cytochrome P-450-dependent oxidation of arachidonic acid to 16-, 17-, and 18-hydroxyeicosatetraenoic acids

Incubation of rat liver microsomal fractions with arachidonic acid in the presence of NADPH results in the formation of three novel monohydroxylated fatty acid metabolites. Utilizing chromatographic and mass spectral techniques, these metabolites have been identified as 16-, 17-, and 18-hydroxyeicosatetraenoic acids. The NADPH-dependent microsomal metabolism of arachidonic acid to 16-, 17-, 18-, and 19-hydroxyeicosatetraenoic acids is induced after animal treatment with beta-naphthoflavone. Reconstitution of the arachidonic acid oxygenase utilizing individual purified cytochrome P-450 enzymes demonstrates regioselectivity, controlled by the protein catalyst, for the hydroxylation of the sp3 carbon atoms adjacent to the methyl end of the fatty acid.     

Rapid in vitro ectomycorrhizal infection onPinus densiflora roots byTricholoma matsutake

The root systems of 11-wk-oldPinus densiflora seedlings were inoculated with a hyphal suspension ofTricholoma matsutake and aseptically incubated for 4 wk in a forest soil without supplying exogenous carbohydrates. One week following inoculation, fungal hyphae had colonized the root surface and bound soil particles together establishing a root-substrate continuum. Fungal hyphae were visible within the main root cortex following clearing bleaching and staining. In the ensuing days, fungal colonization was observed within elongating lateral roots in which Hartig net formation was confirmed 4 wk after inoculation. This is the first report of rapid ectomycorrhizal infection ofP. densiflora seedings byT. matsutake.     

Epstein-Barr virus lytic replication elicits ATM checkpoint signal transduction while providing an S-phase-like cellular environment

When exposed to genotoxic stress, eukaryotic cells demonstrate a DNA damage response with delay or arrest of cell-cycle progression, providing time for DNA repair. Induction of the Epstein-Barr virus (EBV) lytic program elicited a cellular DNA damage response, with activation of the ataxia telangiectasia-mutated (ATM) signal transduction pathway. Activation of the ATM-Rad3-related (ATR) replication checkpoint pathway, in contrast, was minimal. The DNA damage sensor Mre11-Rad50-Nbs1 (MRN) complex and phosphorylated ATM were recruited and retained in viral replication compartments, recognizing newly synthesized viral DNAs as abnormal DNA structures. Phosphorylated p53 also became concentrated in replication compartments and physically interacted with viral BZLF1 protein. Despite the activation of ATM checkpoint signaling, p53-downstream signaling was blocked, with rather high S-phase CDK activity associated with progression of lytic infection. Therefore, although host cells activate ATM checkpoint signaling with response to the lytic viral DNA synthesis, the virus can skillfully evade this host checkpoint security system and actively promote an S-phase-like environment advantageous for viral lytic replication.     

Formation of Mycorrhiza-like Structures in Cultured Root/Callus of Cathaya argyrophylla Chun et Kuang Infected with the Ectomycorrhizal Fungus Cenococcum geophilum Fr.

An in vitro system was used for ectomycorrhizal synthesis of Cenococcum geophilum Fr. with Cathaya argyrophylla Chun et Kuang, an endangered species. Calli initiated from stem segments and adventitious roots differentiated from young seedlings were removed and cocultured with Cenococcum geophllum on a modified Murashlge-Skoog medium. Fungal hyphae were visible within intercellular spaces of the callus 4 weeks after inoculation, but definite and well-developed Hartig net structures did not form in the calU 8 weeks after inoculation. The typical ectomycorrhizal structures （i.e. hyphal mantle and Intracortical Hartig net） were observed in root segments 8 weeks after inoculation. This is the first report of aseptic ectomycorrhlzal-like formation/infection between root organ/callus of Cathaya argyrophylla and the ectomycorrhizal fungus Cenococcum geophflum. This culture system is useful for further investigation of mycorrhizal synthesis in Cathaya trees.     

Dynamic evolution of eukaryotic mitochondrial and nuclear genomes: a case study in the gourmet pine mushroom Tricholoma matsutake

Fungi, as eukaryotic organisms, contain two genomes, the mitochondrial genome and the nuclear genome, in their cells. How the two genomes evolve and correlate to each other is debated. Herein, taking the gourmet pine mushroom Tricholoma matsutake as an example, we performed comparative mitogenomic analysis using samples collected from diverse locations and compared the evolution of the two genomes. The T. matsutake mitogenome encodes 49 genes and is rich of repetitive and non-coding DNAs. Six genes were invaded by up to 11 group I introns, with one cox1 intron cox1P372 showing presence/absence dynamics among different samples. Bioinformatic analyses suggested limited or no evidence of mitochondrial heteroplasmy. Interestingly, hundreds of mitochondrial DNA fragments were found in the nuclear genome, with several larger than 500 nt confirmed by PCR assays and read count comparisons, indicating clear evidence of transfer of mitochondrial DNA into the nuclear genome. Nuclear DNA of T. matsutake showed a higher mutation rate than mitochondrial DNA. Furthermore, we found evidence of incongruence between phylogenetic trees derived from mitogenome and nuclear DNA sequences. Together, our results reveal the dynamic genome evolution of the gourmet pine mushroom.