A Quantitative Real-Time PCR Method to Detect the Quinoa Downy Mildew Pathogen, Peronospora variabilis

Quinoa downy mildew, caused by Peronospora variabilis, is the most devastating disease of quinoa globally. Rapid, sensitive diagnostic methods are needed to detect and quantify this pathogen in seeds and plant tissue. A hydrolysis probe-based quantitative real-time PCR (qPCR) assay including a competitive internal control was developed for P. variabilis detection. This assay could detect as low as 20 ag of DNA or approximately 25 internal transcribed spacer (ITS) copies per reaction with efficiencies ranging from 93.9 to 98.2%. No non-target amplification was observed when tested against DNA from other downy mildew pathogens and related oomycetes. Peronospora variabilis strains from multiple countries were detected using this assay. The assay was successfully applied to quantify the pathogen in quinoa seeds from a field trial conducted in Washington State. Downy mildew disease was recorded on all 14 genotypes with the genotypes 104.88 and 106.49 recording the highest area under the disease progress values (3,236 ± 303 SE and 2,851 ± 198, respectively) while J6 and Dutchess recorded the lowest (441 ± 107 and 409 ± 129, respectively). Seed washes obtained from field samples were subjected to the qPCR assay, and the pathogen was detected in all samples. The highest pathogen ITS copy number recorded with 106.49 (194,934 ± 38,171 SE), while the lowest was observed in Pasto (5,971 ± 1,435) and Riobamba (9,954 ± 4,243). This qPCR assay could lead to improved detection and quantification of P. variabilis as well as increased understanding of quinoa-P. variabilis interactions and epidemiology.

A Quantitative PCR Method to Detect the Tomato Corky Root Rot Pathogens, Pseudopyrenochaeta lycopersici and P. terrestris

Corky root rot is an important disease in tomato production systems and is caused by Pseudopyrenochaeta terrestris and P. lycopersici (formerly Pyrenochaeta lycopersici Types 1 and 2, respectively). The corky root rot pathogens are slow growing and difficult to isolate and quantify in soil and plant tissue. A multiplex hydrolysis probe-based qPCR assay was designed to allow for simultaneous detection and quantification of P. lycopersici and P. terrestris with a competitive internal control to indicate if qPCR inhibitors are present. Single species and multiplex assays for Pseudopyrenochaeta spp. detected DNA levels above 0.013 pg of DNA per reaction. These highly specific assays had no nontarget amplification of other fungal and oomycete pathogens or rhizosphere-associated fungi of tomatoes that were tested. This assay can be used to quantify Pseudopyrenochaeta populations in roots and soils in tomato production systems to better determine the impacts of disease management strategies on Pseudopyrenochaeta spp. and provides a tool to study the biology of Pseudopyrenochaeta spp.

The conserved asparagine and arginine are essential for catalysis of mammalian adenylyl cyclase

Mammalian adenylyl cyclases have two homologous cytoplasmic domains (C1 and C2), and both domains are required for the high enzymatic activity. Mutational and genetic analyses of type I and soluble adenylyl cyclases suggest that the C2 domain is catalytically active and the C1 domain is not; the role of the C1 domain is to promote the catalytic activity of the C2 domain. Two amino acid residues, Asn-1025 and Arg-1029 of type II adenylyl cyclase, are conserved among the C2 domains, but not among the C1 domains, of adenylyl cyclases with 12 putative transmembrane helices. Mutations at each amino acid residue alone result in a 30-100-fold reduction in Kcat of adenylyl cyclase. However, the same mutations do not affect the Km for ATP, the half-maximal concentration (EC50) for the C2 domain of type II adenylyl cyclase to associate with the C1 domain of type I adenylyl cyclase and achieve maximal enzyme activity, or the EC50 for forskolin to maximally activate enzyme activity with or without Gsalpha. This indicates that the mutations at these two residues do not cause gross structural alteration. Thus, these two conserved amino acid residues appear to be crucial for catalysis, and their absence from the C1 domains may account for its lack of catalytic activity. Mutations at both amino acid residues together result in a 3,000-fold reduction in Kcat of adenylyl cyclase, suggesting that these two residues have additive effects in catalysis. A second site suppressor of the Asn-1025 to Ser mutant protein has been isolated. This suppressor has 17-fold higher activity than the mutant and has a Pro-1015 to Ser mutation.

An electron-capture gas-liquid-chromatographic method for the determination of prostaglandin F2alpha in biological fluids

A sensitive electron-capture gas-liquid-chromatographic method for the determination of sub-nanogram quantities of prostaglandin F(2alpha) was developed. The method is based on the sub-microgram scale conversion of the prostaglandin into the electron-capturing pentafluorobenzyl ester, and analysis of the latter as the tris-trimethylsilyl ether. The lower limit of detection was 12.5pg of the ester injected ;on-column' as the silylated product. The method was successfully applied to the determination of prostaglandin F(2alpha) in monkey plasma. The specificity of the analytical procedure was increased by incorporating a thin-layer chromatographic fractionation before gas-liquid chromatography. The utility of the analytical methodology developed was demonstrated by its application to the determination of plasma concentrations of intact prostaglandin F(2alpha) in a Rhesus monkey, after subcutaneous administration of a single dose of prostaglandin F(2alpha). The electron-capture gas-liquid-chromatographic assay is compared with the radioimmunoassay and the gas-liquid-chromatographic-mass-spectrometry assay for the determination of prostaglandin F(2alpha).