Finished Genome of the Fungal Wheat Pathogen Mycosphaerella graminicola Reveals Dispensome Structure, Chromosome Plasticity, and Stealth Pathogenesis.

The plant-pathogenic fungus Mycosphaerella graminicola (asexual stage: Septoria tritici) causes septoria tritici blotch, a disease that greatly reduces the yield and quality of wheat. This disease is economically important in most wheat-growing areas worldwide and threatens global food production. Control of the disease has been hampered by a limited understanding of the genetic and biochemical bases of pathogenicity, including mechanisms of infection and of resistance in the host. Unlike most other plant pathogens, M. graminicola has a long latent period during which it evades host defenses. Although this type of stealth pathogenicity occurs commonly in Mycosphaerella and other Dothideomycetes, the largest class of plant-pathogenic fungi, its genetic basis is not known. To address this problem, the genome of M. graminicolawas sequenced completely. The finished genome contains 21 chromosomes, eight of which could be lost with no visible effect on the fungus and thus are dispensable. This eight-chromosome dispensome is dynamic in field and progeny isolates, is different from the core genome in gene and repeat content, and appears to have originated by ancient horizontal transfer from an unknown donor. Synteny plots of the M. graminicola chromosomes versus those of the only other sequenced Dothideomycete, Stagonospora nodorum, revealed conservation of gene content but not order or orientation, suggesting a high rate of intra-chromosomal rearrangement in one or both species. This observed “mesosynteny” is very different from synteny seen between other organisms. A surprising feature of the M. graminicolagenome compared to other sequenced plant pathogens was that it contained very few genes for enzymes that break down plant cell walls, which was more similar to endophytes than to pathogens. The stealth pathogenesis of M. graminicola probably involves degradation of proteins rather than carbohydrates to evade host defenses during the biotrophic stage of infection and may have evolved from endophytic ancestors

Evolutionary Dynamics of Mating-Type Loci of Mycosphaerella spp. Occurring on Banana▿ †

The devastating Sigatoka disease complex of banana is primarily caused by three closely related heterothallic fungi belonging to the genus Mycosphaerella: M. fijiensis, M. musicola, and M. eumusae. Previous phylogenetic work showing common ancestry led us to analyze the mating-type loci of these Mycosphaerella species occurring on banana. We reasoned that this might provide better insight into the evolutionary history of these species. PCR and chromosome-walking approaches were used to clone the mating-type loci of M. musicola and M. eumusae. Sequences were compared to the published mating-type loci of M. fijiensis and other Mycosphaerella spp., and a novel organization of the MAT loci was found. The mating-type loci of the examined Mycosphaerella species are expanded, containing two additional Mycosphaerella-specific genes in a unique genomic organization. The proteins encoded by these novel genes show a higher interspecies than intraspecies homology. Moreover, M. fijiensis, M. musicola, and M. eumusae contain two additional mating-type-like loci, containing parts of both MAT1-1-1 and MAT1-2-1. The data indicate that M. fijiensis, M. musicola, and M. eumusae share an ancestor in which a fusion event occurred between MAT1-1-1 and MAT1-2-1 sequences and in which additional genes became incorporated into the idiomorph. The new genes incorporated have since then evolved independently in the MAT1-1 and MAT1-2 loci. Thus, these data are an example of the evolutionary dynamics of fungal MAT loci in general and show the great flexibility of the MAT loci of Mycosphaerella species in particular

Control of Mycosphaerella graminicola on Wheat Seedlings by Medical Drugs Known To Modulate the Activity of ATP-Binding Cassette Transporters▿

Medical drugs known to modulate the activity of human ATP-binding cassette (ABC) transporter proteins (modulators) were tested for the ability to potentiate the activity of the azole fungicide cyproconazole against in vitro growth of Mycosphaerella graminicola and to control disease development due to this pathogen on wheat seedlings. In vitro modulation of cyproconazole activity could be demonstrated in paper disk bioassays. Some of the active modulators (amitriptyline, flavanone, and phenothiazines) increased the accumulation of cyproconazole in M. graminicola, suggesting that they reversed cyproconazole efflux. However, synergism between cyproconazole and modulators against M. graminicola on wheat seedlings could not be shown. Despite their low in vitro toxicity to M. graminicola, some modulators (amitriptyline, loperamide, and promazine) did show significant intrinsic disease control activity in preventive and curative foliar spray tests with wheat seedlings. The results suggest that these compounds have indirect disease control activity based on modulation of fungal ABC transporters essential for virulence and constitute a new class of disease control agents

7.Econ.concorrenza e regolazione_AeGI 2015_2016_2 PP

<div><p>Black Sigatoka or black leaf streak disease, caused by the Dothideomycete fungus <i>Pseudocercospora fijiensis</i> (previously: <i>Mycosphaerella fijiensis</i>), is the most significant foliar disease of banana worldwide. Due to the lack of effective host resistance, management of this disease requires frequent fungicide applications, which greatly increase the economic and environmental costs to produce banana. Weekly applications in most banana plantations lead to rapid evolution of fungicide-resistant strains within populations causing disease-control failures throughout the world. Given its extremely high economic importance, two strains of <i>P</i>. <i>fijiensis</i> were sequenced and assembled with the aid of a new genetic linkage map. The 74-Mb genome of <i>P</i>. <i>fijiensis</i> is massively expanded by LTR retrotransposons, making it the largest genome within the Dothideomycetes. Melting-curve assays suggest that the genomes of two closely related members of the Sigatoka disease complex, <i>P</i>. <i>eumusae</i> and <i>P</i>. <i>musae</i>, also are expanded. Electrophoretic karyotyping and analyses of molecular markers in <i>P</i>. <i>fijiensis</i> field populations showed chromosome-length polymorphisms and high genetic diversity. Genetic differentiation was also detected using neutral markers, suggesting strong selection with limited gene flow at the studied geographic scale. Frequencies of fungicide resistance in fungicide-treated plantations were much higher than those in untreated wild-type <i>P</i>. <i>fijiensis</i> populations. A homologue of the <i>Cladosporium fulvum Avr4</i> effector, <i>PfAvr4</i>, was identified in the <i>P</i>. <i>fijiensis</i> genome. Infiltration of the purified PfAVR4 protein into leaves of the resistant banana variety Calcutta 4 resulted in a hypersensitive-like response. This result suggests that Calcutta 4 could carry an unknown resistance gene recognizing PfAVR4. Besides adding to our understanding of the overall Dothideomycete genome structures, the <i>P</i>. <i>fijiensis</i> genome will aid in developing fungicide treatment schedules to combat this pathogen and in improving the efficiency of banana breeding programs.</p></div

Comparison of the amount of repeat-induced point mutation (RIP) between AT-rich blocks and more GC-rich regions of the <i>Pseudocercospora fijiensis</i> genome as measured by the RIP index (CpA+TpG)/(ApC+GpT).

<p>(A) AT-rich blocks have a lower RIP index indicating a depletion of RIP-susceptible sites due to a higher frequency of RIP compared to (B) an AT-poor region (higher GC) of the genome, which has a higher RIP index reflecting very little RIP. Four AT-rich blocks are shown along with one AT-poor region for comparison. Length of each block in kilobases is shown along the x-axis and the RIP index (CpA+TpG)/(ApC+GpT) is shown on the y-axis.</p

Comparison of repeat classes among <i>Zymoseptoria tritici</i>, the only Dothideomycete with a completely sequenced genome, <i>Pseudocercospora fijiensis</i> and <i>Cladosporium fulvum</i>, the only other Dothideomycete known to have a transposon-expanded genome.

<p>Comparison of repeat classes among <i>Zymoseptoria tritici</i>, the only Dothideomycete with a completely sequenced genome, <i>Pseudocercospora fijiensis</i> and <i>Cladosporium fulvum</i>, the only other Dothideomycete known to have a transposon-expanded genome.</p

The repeat-induced point mutation (RIP) index calculated as (CpA+TpG)/(ApC+GpT) for genes^a and repeats^a in AT-poor and–rich regions of the <i>Pseudocercospora fijiensis</i> genome.

<p>The repeat-induced point mutation (RIP) index calculated as (CpA+TpG)/(ApC+GpT) for genes<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005876#t002fn001" target="_blank">^a</a> and repeats<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005876#t002fn001" target="_blank">^a</a> in AT-poor and–rich regions of the <i>Pseudocercospora fijiensis</i> genome.</p

Comparison of selected gene families with potential roles in pathogenicity among five Dothideomycete fungi and the saprotrophic Sordariomycete <i>Neurospora crassa</i>.

<p>Comparison of selected gene families with potential roles in pathogenicity among five Dothideomycete fungi and the saprotrophic Sordariomycete <i>Neurospora crassa</i>.</p

Electrophoretic karyotypes of two strains of <i>Pseudocercospora fijiensis</i>.

<p>A) Bands separated with conditions for small chromosomes. Lane 1, chromosomes from <i>Saccharomyces cerevisiae</i> as high-molecular-weight (HMW) marker; lane 2, strain CIRAD86; lane 3, strain E22. B) Bands separated under conditions to resolve medium and large chromosomes. Lane 1, chromosomes from <i>Schizosaccharomyces pombe</i> as HMW marker for large chromosomes; lane 2, strain CIRAD86; lane 3, strain E22; lane 4, chromosomes from <i>Hansenula wingei</i> as HMW marker for medium chromosomes in size. Marker sizes are in Kb.</p