茶树DNA去甲基化酶基因的全基因组鉴定及表达分析

DNA去甲基化酶(dMTase)是主动去甲基化过程中具有糖基化酶和脱嘌呤裂合酶活性的双功能酶.基于茶树基因组数据,本研究利用生物信息学方法对茶树DNA去甲基化酶(CsdMTase)编码基因进行了全面鉴定和序列分析.全基因组鉴定结果表明,舒茶早基因组中包含4个CsdMTases,系统进化分析将CsdMTases分为DME...     

Pisatin demethylation by fungal pathogens and nonpathogens of pea: association with pisatin tolerance and virulence

Previous studies have indicated that detoxification of their hosts' phytoalexins is a tolerance mechanism for some true fungi, but not the fungus-like Oomycota, and may be involved in determining the virulence of a pathogen. In the present study, the associations between demethylation of the pea phytoalexin pisatin, tolerance to pisatin, and virulence on pea were examined for 50 fungal isolates which represent 17 species of pathogens and nonpathogens of pea. All isolates ofPythium coloratum and P. irregulare failed to metabolize and were sensitive to pisatin, consistent with previous observations that members of the Oomycota generally lack the ability to metabolize and are sensitive to their hosts' phytoalexins. Among true fungi tested, the ability to demethylate pisatin was common, regardless of whether the particular isolate was pathogenic on pea or not. However, when the rate of pisatin demethylation was compared to virulence, all but one of the moderate to highly virulent isolates rapidly demethylated pisatin. In addition, the more rapidly demethylating isolates were generally more tolerant of pisatin. These results suggest that a specialized enzyme system for quickly detoxifying pisatin might be present in most pea pathogens. In previous studies a specific cytochrome P450 enzyme for demethylating pisatin was identified in the pea pathogen Nectria haematococca mating population VI, and genes (PDA genes) encoding that enzyme have been cloned from this fungus. When DNA specific for these genes was used to probe genomic DNA from other fungi that demethylate pisatin, significant hybridization was detected with only one fungus, the pea pathogen Fusarium oxysporum f. sp. pisi. If the other pea pathogens possess a specific cytochrome P450 system for detoxification of pisatin, the genes encoding these enzymes apparently share limited nucleotide similarity with N. haematococca PDA genes.     

Activities of biotransformation enzymes in pheasant (Phasianus colchicus) and their modulation by in vivo administration of mebendazole and flubendazole

Basal activities of certain pheasant hepatic and intestinal biotransformation enzymes and modulation of their activities by anthelmintics flubendazole (FLBZ) and mebendazole (MBZ) were investigated in subcellular fractions that were prepared from liver and small intestine of control and FLBZ or MBZ treated birds. Several oxidation, reduction and conjugation enzyme activities were assessed. In the liver, treatment of pheasants by FLBZ or MBZ caused very slight or no changes in monooxygenase activities and conjugation enzymes. More significative changes were detected in small intestine. Metyrapone and daunorubicin reductase activities were increased by both substances in the liver. This is the first evidence that certain benzimidazoles modulate reductases of carbonyl group. With respect to the relatively slight extent of the changes caused by FLBZ or MBZ we can assume that repeated administration of therapeutic doses of both FLBZ and MBZ has probably no serious influence on pheasant biotransformation enzyme system.     

New tools for studying epidemiology and resistance of grape powdery mildew to DMI fungicides

Using a Random Amplified Polymorphic DNA (RAPD) assay, we investigated the genetic polymorphism existing among 62 European isolates of the grape powdery mildew fungus (Uncinula necator [Schw.] Burr.). Isolates overwintering as mycelium in buds were genetically distinct from isolates overwintering as ascospores, suggesting the existence of two genetically isolated powdery mildew populations, and consequently of two independent sources of inoculum in the vineyard. Isolates resistant to fungicides inhibiting sterol 14α-demethylation (DMIs) were found in both populations, suggesting that resistance to DMIs may arise independently in the two powdery mildew populations. A PCR assay targeting the gene encoding U. necator 14α-demethylase has been developed which will permit an early, specific detection of U. necator infections, and may be useful for spraying programmes. ©1997 SCI     

A comparative molecular field analysis study of obtusifoliol 14α-methyl demethylase inhibitors

This report describes the development of a Comparative Molecular Field Analysis (CoMFA) model from a set of obtusifoliol 14α-methyl demethylase (DM) inhibitors to aid in the design of herbicides targeting sterol biosynthesis. CoMFA is a three-dimensional (3-D) quantitative structure–activity relationship (QSAR) method that is useful in the probing of receptor binding sites when experimental structure data are unavailable. Conformational analysis and SAR of some rigid and active analogs were used to build the initial model using the active analog hypothesis. The model was subsequently used to design compounds that retain the active site shape requirements, but incorporate physical properties that favor soil-applied herbicidal action. In addition, a second-generation CoMFA model incorporating the newly designed inhibitors was developed and represents the current understanding of the DM binding site. This model was derived from a pharmacophore developed from two methods, the active analog approach as well as from the Catalyst program. The fact that two independent methods produced a similar pharmacophore strengthens the validity of the model. © 1999 Society of Chemical Industry     

Does agricultural use of azole fungicides contribute to resistance in the human pathogen Aspergillus fumigatus?

Azole resistance in human fungal pathogens has increased over the past twenty years, especially in immunocompromised patients. Similarities between medical and agricultural azoles, and extensive azole (14α‐demethylase inhibitor, DMI) use in crop protection, prompted speculation that resistance in patients with aspergillosis originated in the environment. Aspergillus species, and especially Aspergillus fumigatus, are the largest cause of patient deaths from fungi. Azole levels in soils following crop spraying, and differences in sensitivity between medical and agricultural azoles (DMIs), indicate weaker selection in cropping systems than in patients receiving azole therapy. Most fungi have just one CYP51 paralogue (isozyme CYP51B), but in Aspergillus sp. mutations conferring azole resistance are largely confined to a second paralogue, CYP51A. Binding within the active centre is similar for medical and agricultural azoles but differences elsewhere between the two paralogues may ensure selection depends on the DMI used on crops. Two imidazoles, imazalil and prochloraz, have been widely used since the early 1970s, yet unlike triazoles they have not been linked to resistance in patients. Evidence that DMIs are the origin, or increase the frequency, of azole resistance in human fungal pathogens is lacking. Limiting DMI use would have serious impacts on disease control in many crops, and remove key tools in anti‐resistance strategies. © 2017 Society of Chemical Industry     

Involvement of cytochrome P‐450 enzyme activity in the selectivity and safening action of pyrazosulfuron‐ethyl

To investigate the selectivity and safening action of the sulfonylurea herbicide pyrazosulfuron‐ethyl (PSE), pyrazosulfuron‐ethyl O‐demethylase (PSEOD) activity involving oxidative metabolism by cytochrome P‐450 was studied in rice (Oryza sativa L cv Nipponbare) and Cyperus serotinus Rottb. Cytochrome P‐450‐dependent activity was demonstrated by the use of the inducers 1,8‐naphthalic anhydride and ethanol, the herbicides PSE, bensulfuron‐methyl, dimepiperate and dymron, or the inhibitor piperonyl butoxide (PBO). Growth inhibition in C serotinus seedlings was more severe than that in rice seedlings. O‐Dealkylation activities of PSE were induced differently in rice and in C serotinus, with distinctly higher activity in rice seedlings. The induced PSEOD activities were slightly inhibited by PBO in rice seedlings, whereas they were strongly inhibited in C serotinus seedlings. Dimepiperate and dymron were effective safeners of rice against PSE treatment. Treatments with herbicide alone resulted in less induction of PSEOD activity compared with combined treatments of the herbicide and safener. PSEOD activity in rice seedlings induced with herbicide alone was strongly inhibited by PBO, whereas it was weakly inhibited in rice seedlings induced with combinations of PSE and two safeners. These results suggest that O‐demethylation by cytochrome P‐450 enzymes may be involved in the metabolism of PSE and may contribute to its selectivity and safening action. Furthermore, these results suggest the existence of a multiple form of cytochrome P‐450 in plants. © 2001 Society of Chemical Industry