Plant Pathogenic Fungus Magnaporthe Grisea Research Articles

Genome Resource of Sphingomonas carotinifaciens L9-754T, an Endophyte Isolated From Leaf Tissues of Jatropha curcas.

Sphingomonas carotinifaciens strain L9-754T (DSM 27347) is a gram-negative, chemoheterotrophic, and rod-shaped endophyte isolated from the stem tissues of Jatropha curcas L. This strain has putative in vitro antagonistic ability against the plant pathogenic fungus Magnaporthe grisea. A draft genome of L9-754T was obtained using the PacBio SMRT cell platform. By analyzing the genome of strain L9-754T, a gene cluster (GQR91_18700 - GQR91_18715) related to an antioxidant enzyme was identified in the obtained draft genome. The information obtained from the draft genome is expected to reveal the putative properties helpful in biocontrol applications.

TheMagnaporthe griseaclass VII chitin synthase is required for normal appressorial development and function

The plant pathogenic fungus Magnaporthe grisea is able to enter its host via appressorium-mediated penetration. Earlier investigations have shown that these infection structures are rich in the cell wall polysaccharide chitin. Previously, we have described how the transcription of a class VII chitin synthase-encoding gene CHS7 is completely dependent on the putative transcription factor Con7p during the germination of conidia, and how con7(-) mutants are unable to form appressoria under any conditions tested. Because of the pleiotropic effects of the con7(-) mutation, we examined the consequences of the targeted deletion of CHS7. The chs7(-) mutants generated were unable to form appressoria on artificial surfaces, except following the application of the exogenous inducers 1,16-hexadecanediol and cyclic adenosine monophosphate. The appressoria formed had a reduced chitin content and were often found to be smaller and misshapen compared with the wild-type. chs7(-) mutants were significantly reduced in their ability to enter rice plants, but growth in planta was not affected. Reverse transcriptase-polymerase chain reaction analysis demonstrated that CHS7 transcription was strongly induced on germination of spores, and a green fluorescent protein-tagged Chs7p protein was found to be produced abundantly during infection-related morphogenesis. Together, these data suggest that the class VII chitin synthase Chs7p of M. grisea is required for normal appressorium formation and function.

Siderophore synthesis in Magnaporthe grisea is essential for vegetative growth, conidiation and resistance to oxidative stress

The plant pathogenic fungus Magnaporthe grisea excretes siderophores of the coprogen-type for iron acquisition and uses ferricrocin for intracellular iron storage. In the present report we characterize mutants with defects in extracellular siderophore biosynthesis. Deletion of the M. grisea SSM2 gene, which encodes a non-ribosomal peptide synthetase, resulted in a loss of the production of all coprogens. The mutant strains had a reduced growth rate, produced fewer conidia and were more sensitive to oxidative stress. Ferricrocin production was not affected. Upon deletion of M. grisea OMO1, a gene predicted to encode an l-ornithine- N 5-monooxygenase, no siderophores of any type were detected, the strain was aconidial, growth rate was reduced and sensitivity to oxidative stress was increased. Abundance of several proteins was affected in the mutants. The Δssm2 and Δomo1 mutant phenotypes were complemented by supplementation of the medium with siderophores or reintroduction of the respective genes.

Tps1 regulates the pentose phosphate pathway, nitrogen metabolism and fungal virulence.

Trehalose fulfils a wide variety of functions in cells, acting as a stress protectant, storage carbohydrate and compatible solute. Recent evidence, however, indicates that trehalose metabolism may exert important regulatory roles in the development of multicellular eukaryotes. Here, we show that in the plant pathogenic fungus Magnaporthe grisea trehalose-6-phosphate (T6P) synthase (Tps1) is responsible for regulating the pentose phosphate pathway, intracellular levels of NADPH and fungal virulence. Tps1 integrates glucose-6-phosphate (G6P) metabolism with nitrogen source utilisation, and thereby regulates the activity of nitrate reductase. Activity of Tps1 requires an associated regulator protein Tps3, which is also necessary for pathogenicity. Tps1 controls expression of the nitrogen metabolite repressor gene, NMR1, and is required for expression of virulence-associated genes. Functional analysis of Tps1 indicates that its regulatory functions are associated with binding of G6P, but independent of Tps1 catalytic activity. Taken together, these results demonstrate that Tps1 is a central regulator for integration of carbon and nitrogen metabolism, and plays a pivotal role in the establishment of plant disease.

Mining the gene repertoire and ESTs for G protein‐coupled receptors with evolutionary perspective

The purpose of this article was to review recent progress in mining the gene repertoire and expressed sequence tags (ESTs) for the super-family of G protein-coupled receptors (GPCRs) in the form of a proceeding from the Nordic GPCR meeting held at the Nobel Forum, Karolinska Institute in August 2006. We update and give an overview of the expansion of the main families of GPCRs; Glutamate, Rhodopsin, Adhesion, Frizzled and Secretin (GRAFS) in perspective of fully sequenced genomes. We look into the most recent findings including the work that has been carried out on the spotted green puffer fish (Tetraodon nigroviridis), mouse (Mus musculus), chicken (Gallus gallus), slime mold (Dictyostelium discoideum) and the plant pathogenic fungus Magnaporthe grisea. We use examples from our recent work on chicken GPCRs to highlight the importance of detailed assembly and curation of sequences and how that can affect percentage similarity and phylogeny. ESTs can give valuable information about expression patterns. GPCRs have comparatively low numbers of EST suggesting that GPCRs are in generally expressed in lower amount than other genes. We discuss similarities in the evolution of the trace amine associated receptors with other sensory receptors.

Diterpenoids from Coprinus heptemerus.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Diterpenoids from Coprinus heptemerus

Seven diterpenoids, isolated due to their ability to inhibit spore germination in the plant pathogenic fungus Magnaporthe grisea, were obtained from cultures of the basidiomycete Coprinus heptemerus. The structures of the compounds, named heptemerones A–G, were determined with spectroscopic techniques.

Novel G-protein-coupled receptor-like proteins in the plant pathogenic fungus Magnaporthe grisea

An analysis of the Magnaporthe grisea genome and comparison with other fungi identified homologs of known G protein-coupled receptor-like proteins and a novel class of GPCR-like receptors in M. grisea that are specific to filamentous ascomycete fungi.

The glyoxylate cycle is required for temporal regulation of virulence by the plant pathogenic fungus Magnaporthe grisea.

We describe the isolation and characterization of ICL1 from the rice blast fungus Magnaporthe grisea, a gene that encodes isocitrate lyase, one of the principal enzymes of the glyoxylate cycle. ICL1 shows elevated expression during development of infection structures and cuticle penetration, and a targeted gene replacement showed that the gene is required for full virulence by M. grisea. In particular, we found that the prepenetration stage of development, before entry into plant tissue, is affected by loss of the glyoxylate cycle. There is a delay in germination, infection-related development and cuticle penetration in Delta icl1 mutants. Recent reports have shown the importance of the glyoxylate cycle in the virulence of the human pathogenic fungus Candida albicans and the bacterial pathogen Mycobacterium tuberculosis. Our results indicate that the glyoxylate cycle is also important in this plant pathogenic fungus, demonstrating the widespread utility of the pathway in microbial pathogenesis.

Repeat-induced point mutation (RIP) in Magnaporthe grisea: implications for its sexual cycle in the natural field context.

Repeat-induced point mutation (RIP) is a process that detects DNA duplications and peppers their sequences with C:G to T:A transitions in the sexual phase of the life cycle. So far, this unique mechanism has been identified as a currently active process in only two fungal species, Neurospora crassa and Podospora anserina. To determine whether a RIP-like process operates in the plant pathogenic fungus Magnaporthe grisea, the retrotransposon MAGGY and the hygromycin B phosphotransferase gene were introduced into the fungus as multiple transgenes and examined for sequence alterations after a cross. Frequent C:G to T:A transitions in the transgenes were found in the descendants, preferentially in (A/Tp)Cp(A/T)contexts, suggesting that a process similar to RIP functions in M.grisea. We also examined the sequence of another retrotransposon Pyret in six field isolates of M. grisea. Even though no perfect stage has been known in M. grisea under field conditions to date, RIP-like transitions were found in all the field isolates tested. Interestingly, the frequency of the transitions mostly correlated with the fertility of the isolates examined under laboratory conditions. These results imply that the sexual cycle of this fungus exists or existed in the natural field context.

Heat shock, copper sulfate and oxidative stress activate the retrotransposon MAGGY resident in the plant pathogenic fungus Magnaporthe grisea.

MAGGY is a gypsy-like retrotransposon isolated from the plant pathogenic fungus Magnaporthe grisea. The ability of various stresses to activate MAGGY was tested in the original and in a heterologous host (Colletotrichum lagenarium), using beta-glucuronidase (GUS) as a reporter. The MAGGY promoter was activated in M. grisea by either heat shock, copper sulfate, or oxidative stress, but not by the antifungal substance p-coumaric acid. Transcriptional up-regulation of MAGGY RNA was also observed following heat shock and oxidative stress. The MAGGY promoter remained responsive to the above-mentioned stresses when transformed into a M. grisea isolate that had no endogenous MAGGY elements. In C. lagenarium, however, the MAGGY promoter showed only basal expression of GUS and no further up-regulation was induced by any of the stress treatments, suggesting that the stress-responding cis-element(s) in the MAGGY promoter is not functional in a wider range of fungi. The relationship between the activation of MAGGY by stress and phenotypic diversification in M. grisea, including variations in pathogenicity, is discussed.

A telomeric avirulence gene determines efficacy for the rice blast resistance gene Pi-ta.

Genetic mapping showed that the rice blast avirulence gene AVR-Pita is tightly linked to a telomere on chromosome 3 in the plant pathogenic fungus Magnaporthe grisea. AVR-Pita corresponds in gene-for-gene fashion to the disease resistance (R) gene Pi-ta. Analysis of spontaneous avr-pita(-) mutants indicated that the gene is located in a telomeric 6.5-kb BglII restriction fragment. Cloning and DNA sequencing led to the identification of a candidate gene with features typical of metalloproteases. This gene is located entirely within the most distal 1.5 kb of the chromosome. When introduced into virulent rice pathogens, the cloned gene specifically confers avirulence toward rice cultivars that contain Pi-ta. Frequent spontaneous loss of AVR-Pita appears to be the result of its telomeric location. Diverse mutations in AVR-Pita, including point mutations, insertions, and deletions, permit the fungus to avoid triggering resistance responses mediated by Pi-ta. A point mutation in the protease consensus sequence abolishes the AVR-Pita avirulence function.

CAMP Regulates Infection Structure Formation in the Plant Pathogenic Fungus Magnaporthe grisea.

Magnaporthe grisea, the causal agent of rice blast, is one of the most destructive fungal pathogens of rice throughout the world. Infection of rice by M. grisea requires the formation of an appressorium, a darkly pigmented, dome-shaped structure. The germ tube tip differentiates into an appressorium following germination of conidia on a leaf surface. When conidia germinate on growth medium or other noninductive surfaces, the emerging germ tube does not differentiate and continues to grow vegetatively. Little is known about the endogenous or exogenous signals controlling the developmental process of infection structure formation. We show here that a hydrophobic surface was sufficient for the induction of the appressorium. Furthermore, we demonstrate that the addition of cAMP, its analogs (8-bromo cAMP and N6-monobutyryl cAMP), or 3-isobutyl-1-methylxanthine (an inhibitor of phosphodiesterase) to germinating conidia or to vegetative hyphae induced appressorium formation on noninductive surfaces. The identification of cAMP as a mediator of infection structure formation provides a clue to the regulation of this developmental process. Elucidation of the mechanism involved is not only of biological interest but may also provide the basis for new disease control strategies.

CAMP Regulates Infection Structure Formation in the Plant Pathogenic Fungus Magnaporthe grisea

cAMP Regulates Infection Structure Formation in the Plant Pathogenic Fungus Magnaporthe grisea

Magnaporthe grisea genes for pathogenicity and virulence identified through a series of backcrosses.

We have identified genes for pathogenicity toward rice (Oryza sativa) and genes for virulence toward specific rice cultivars in the plant pathogenic fungus Magnaporthe grisea. A genetic cross was conducted between the weeping lovegrass (Eragrostis curvula) pathogen 4091-5-8, a highly fertile, hermaphroditic laboratory strain, and the rice pathogen O-135, a poorly fertile, female-sterile field isolate that infects weeping lovegrass as well as rice. A six-generation backcrossing scheme was then undertaken with the rice pathogen as the recurrent parent. One goal of these crosses was to generate rice pathogenic progeny with the high fertility characteristic of strain 4091-5-8, which would permit rigorous genetic analysis of rice pathogens. Therefore, progeny strains to be used as parents for backcross generations were chosen only on the basis of fertility. The ratios of pathogenic to nonpathogenic (and virulent to avirulent) progeny through the backcross generations suggested that the starting parent strains differ in two types of genes that control the ability to infect rice. First, they differ by polygenic factors that determine the extent of lesion development achieved by those progeny that infect rice. These genes do not appear to play a role in infection of weeping lovegrass because both parents and all progeny infect weeping lovegrass. Second, the parents differ by simple Mendelian determinants, "avirulence genes," that govern virulence toward specific rice cultivars in all-or-none fashion. Several crosses confirm the segregation of three unlinked avirulence genes, Avr 1-CO39, Avr 1-M201 and Avr1-YAMO, alleles of which determine avirulence on rice cultivars CO39, M201, and Yashiro-mochi, respectively. Interestingly, avirulence alleles of Avr1-CO39, Avr1-M201 and Avr1-YAMO were inherited from the parent strain 4091-5-8, which is a nonpathogen of rice. Middle repetitive DNA sequences ("MGR sequences"), present in approximately 40-50 copies in the genome of the rice pathogen parent, and in very low copy number in the genome of the nonpathogen of rice, were used as physical markers to monitor restoration of the rice pathogen genetic background during introgression of fertility. The introgression of highest levels of fertility into the most successful rice pathogen progeny was incomplete by the sixth generation, perhaps a consequence of genetic linkage between genes for fertility and genes for rice pathogenicity. One chromosomal DNA segment with MGR sequence homology appeared to be linked to the gene Avr1-CO39. Finally, many of the crosses described in this paper exhibited a characteristic common to many crosses involving M. grisea rice pathogen field isolates.(ABSTRACT TRUNCATED AT 400 WORDS)