Draft genome sequences for four isolates of the hemp (Cannabis sativa) fungal pathogen Neofusicoccum parvum.

Four isolates of Neofusicoccum parvum, collected from diseased hemp (Cannabis sativa) plants over a period of 2 years and shown to be pathogenic on C. sativa, were examined in this study. Their genome sizes ranged between 42.8 and 44.4 Mb, with 16,499 ± 72 predicted genes across the four isolates.

Variable genome evolution in fungi after transposon-mediated amplification of a housekeeping gene.

BACKGROUND: Transposable elements (TEs) can be key drivers of evolution, but the mechanisms and scope of how they impact gene and genome function are largely unknown. Previous analyses revealed that TE-mediated gene amplifications can have variable effects on fungal genomes, from inactivation of function to production of multiple active copies. For example, a DNA methyltransferase gene in the wheat pathogen Zymoseptoria tritici (synonym Mycosphaerella graminicola) was amplified to tens of copies, all of which were inactivated by Repeat-Induced Point mutation (RIP) including the original, resulting in loss of cytosine methylation. In another wheat pathogen, Pyrenophora tritici-repentis, a histone H3 gene was amplified to tens of copies with little evidence of RIP, leading to many potentially active copies. To further test the effects of transposon-aided gene amplifications on genome evolution and architecture, the repetitive fraction of the significantly expanded genome of the banana pathogen, Pseudocercospora fijiensis, was analyzed in greater detail. RESULTS: These analyses identified a housekeeping gene, histone H3, which was captured and amplified to hundreds of copies by a hAT DNA transposon, all of which were inactivated by RIP, except for the original. In P. fijiensis the original H3 gene probably was not protected from RIP, but most likely was maintained intact due to strong purifying selection. Comparative analyses revealed that a similar event occurred in five additional genomes representing the fungal genera Cercospora, Pseudocercospora and Sphaerulina. CONCLUSIONS: These results indicate that the interplay of TEs and RIP can result in different and unpredictable fates of amplified genes, with variable effects on gene and genome evolution.

Effectiveness of a Seed Plate Assay for Evaluating Charcoal Rot Resistance in Soybean and the Relationship to Field Performance.

Charcoal rot of soybean, caused by Macrophomina phaseolina, is a disease of economic significance in the United States. Although there are soybean cultivars with moderate resistance, identifying and quantifying resistance is challenging. Existing assays are time consuming, and results are often highly variable. The objectives of this research were to (i) create a reproducible seed plate assay (SPA) for charcoal rot resistance and (ii) correlate field-based disease assessments with SPA results on diverse soybean accessions. To develop the SPA, surface-disinfected seeds from eight soybean genotypes (representing three susceptible and five resistant cultivars) were placed on water agar plates inoculated with M. phaseolina. After incubation at room temperature in darkness for 7 days, percent germination was determined for each cultivar relative to the germination on noninoculated plates. Results from SPA were in general agreement with published responses. None of the soybean genotypes showed complete resistance to M. phaseolina. For the second objective, charcoal rot resistance in 18 soybean accessions was assayed with SPA, and results were analyzed for correlation with field disease assessments from Stuttgart, AR, from 2011 to 2014 and from Rohwer, AR, in 2011 and 2012. SPA consistently categorized soybean genotype resistance compared with field disease assessment averages, and results were consistent with previously published resistance determinations. SPA was significantly correlated with percent height of internal stem discoloration (PHSD) at Stuttgart from 2011 to 2013 and in 2012 at Rohwer, with root and stem severity (RSS) at Rohwer in 2012, and with tap root colonization (CFU) at Stuttgart in 2012. SPA was significantly correlated to yield at Stuttgart in 2011, 2013, and 2014, and in 2011 and 2012 at Rohwer. Yield was not correlated to RSS, PHSD, or CFU at either location or in any year. Therefore, SPA is a reproducible and rapid assay for charcoal rot resistance in soybean and is significantly associated to field performance.

Genome Sequences of Three Races of Peronospora effusa: A Resource for Studying the Evolution of the Spinach Downy Mildew Pathogen.

Downy mildew disease, caused by the obligate oomycete pathogen Peronospora effusa, is the most important economic constraint for spinach production. Three races (races 12, 13, and 14) of P. effusa have been sequenced and assembled. The draft genomes of these three races have been deposited to GenBank and provide useful resources for dissecting the interaction between the host and the pathogen and may provide a framework for determining the mechanism by which new races of the pathogen are rapidly emerging.

Complementation of CTB7 in the Maize Pathogen Cercospora zeina Overcomes the Lack of In Vitro Cercosporin Production.

Gray leaf spot (GLS), caused by the sibling species Cercospora zeina or Cercospora zeae-maydis, is cited as one of the most important diseases threatening global maize production. C. zeina fails to produce cercosporin in vitro and, in most cases, causes large coalescing lesions during maize infection, a symptom generally absent from cercosporin-deficient mutants in other Cercospora spp. Here, we describe the C. zeina cercosporin toxin biosynthetic (CTB) gene cluster. The oxidoreductase gene CTB7 contained several insertions and deletions as compared with the C. zeae-maydis ortholog. We set out to determine whether complementing the defective CTB7 gene with the full-length gene from C. zeae-maydis could confer in vitro cercosporin production. C. zeina transformants containing C. zeae-maydis CTB7 were generated by Agrobacterium tumefaciens-mediated transformation and were evaluated for in vitro cercosporin production. When grown on nitrogen-limited medium in the light-conditions conducive to cercosporin production in other Cercospora spp.-one transformant accumulated a red pigment that was confirmed to be cercosporin by the KOH assay, thin-layer chromatography, and ultra performance liquid chromatography-quadrupole-time-of-flight mass spectrometry. Our results indicated that C. zeina has a defective CTB7, but all other necessary machinery required for synthesizing cercosporin-like molecules and, thus, C. zeina may produce a structural variant of cercosporin during maize infection.