Cloning and expression of cDNA encoding a mitogen-activated protein kinase from a phytopathogenic filamentous fungus

Molecular cloning and characterization of a putative protein kinase gene from the thermophilic fungus Thermomyces lanuginosus

Based on the conserved amino acid sequence (DLKPEN) of serine-threonine protein kinase from several fungi, a degenerate primer was designed and synthesized. Total RNA was isolated from the thermophilic fungus Thermomyces lanuginosus. Using RACE-PCR, full-length cDNA of a putative serine-threonine protein kinase gene was cloned from T. lanuginosus. The full-length cDNA of T. lanuginosus protein kinase was 2551 bp and contained an 1806 bp open reading frame encoding a putative protein kinase precursor of 601 amino acid residues. Sequencing analysis showed that the cloned cDNA of T. lanuginosus had consensus protein kinase sequences. Conservative amino acid subdomains which most serine-threonine kinases contain can be found in the deduced amino acid sequence of T. lanuginosus putative protein kinase. Comparison results showed that the deduced amino acid sequence of T. lanuginosus putative protein kinase was highly homologous to that of Neurospora crassa dis1-suppressing protein kinase Dsk1. The putative protein kinase contained three arginine/serine-rich (SR) regions and two transmembrane domains. These showed that it might be a novel putative serine-threonine protein kinase.

Le.MAPK and its interacting partner, Le.DRMIP, in fruiting body development in Lentinula edodes

Development in shiitake mushroom, Lentinula edodes, is a unique process and studies of the molecular basis of this process may lead to improvement in mushroom cultivation. Previous studies have identified a number of signal transduction genes related to mushroom development, but those genes have not been well characterized. The present work characterized a developmentally regulated MAP kinase, Le.MAPK, and its interaction with a novel gene, Le.DRMIP in the signal transduction pathway. The expression profiles of these two genes reveal their importance in fruiting body initiation and development; the Le.DRMIP transcript is localized predominantly in the developing young fruiting body and gills, which further signifies its role in cell differentiation during mushroom development.

Characterization of HOG1 homologue, CpMK1, from Cryphonectria parasitica and evidence for hypovirus-mediated perturbation of its phosphorylation in response to hypertonic stress

We examined the biological function of cpmk1, which encodes a MAPK of Cryphonectria parasitica, and its regulation by mycovirus. Sequence comparisons revealed that cpmk1 had highest homology with osm1, a hog1-homologue from Magnaporthe grisea. A growth defect was observed in the cpmk1-null mutant under hyperosmotic conditions, indicating that cpmk1 functionally belongs to a hog1 subfamily. Immunoblot analyses indicated that the CpMK1 pathway was affected specifically in hyperosmotic conditions by the hypovirus CHV1-EP713. Moreover, the virus-infected hypovirulent UEP1 strain also exhibited severe osmosensitivity compared to the virus-free isogenic strain EP155/2, thus providing additional evidence for viral regulation of cpmk1 in response to a hypertonic stress. Besides osmosensitivity, disruption of cpmk1 resulted in several, but not all, hypovirulence-associated changes, such as reduced pigmentation, conidiation, laccase production and cryparin expression. However, the cpmk1-null mutant exhibited an increased accumulation of pheromone gene transcripts. Virulence assays of the cpmk1-null mutant revealed reduced canker area, but not as severe as that of UEP1. These results suggest that mycoviruses modulate the MAPK and thereby provoke the aberrant expression of target genes, some of which are likely to be implicated in viral symptom development.

The Fusarium graminearum MAP1 gene is essential for pathogenicity and development of perithecia

SUMMARY Fusarium graminearum is the causal agent of ear blight disease of cereals. Infection occurs at anthesis when ascospores and/or conidia directly penetrate exposed anther and ovary tissue. The hemibiotrophic hyphae colonize floral tissues and developing grains to cause premature ear senescence. During infection, Fusarium hyphae can also produce hazardous trichothecene mycotoxins, thereby posing a threat to human and animal health and safety. The Fusarium MAP1 gene was identified using a PCR approach by its homology to a known pathogenicity gene of Magnaporthe grisea, the mitogen-activated protein kinase gene PMK1. Gene replacement F. graminearum map1 mutants were non-pathogenic on wheat flowers and roots, and also could not infect wounded wheat floral tissue or tomato fruits. Unlike the wild-type strain, map1 mutant inoculations did not compromise grain yield. Map1 mutants lost their ability to form perithecia in vitro, but their rate of asexual conidiation was unaffected. DON mycotoxin production in planta was still detected. Collectively, the observed phenotypes suggest that the Map1 signalling protein controls multiple events in disease establishment and propagation. Novel approaches to control Fusarium ear blight disease by blocking perithecial development are discussed.

Pathogenicity genes of phytopathogenic fungi

Summary Recently many fungal genes have been identified that, when disrupted, result in strains with a reduction or total loss of disease symptoms. Such pathogenicity genes are the subject of this review. The large number of pathogenicity genes identified is due to the application of tagged mutagenesis techniques (random or targeted). Genes have been identified with roles in the formation of infection structures, cell wall degradation, overcoming or avoiding plant defences, responding to the host environment, production of toxins, and in signal cascades. Additionally, genes with no database matches and with 'novel' functions have also been found. Improved technologies for mutation analysis and for sequencing and analysing fungal genomes hold promise for identifying many more pathogenicity genes.

Expression and sequence analysis of the Blumeria graminis mitogen-activated protein kinase genes, mpk1 and mpk2

Mitogen-activated protein (MAP) kinases represent a group of serine/threonine kinases which play a pivotal role in signal transduction processes in eukaryotic cells. Using degenerate PCR primer design based on published and aligned MAP kinase sequences we have cloned and characterised two MAP kinase genes from the barley powdery mildew fungus, Blumeria graminis. We have utilised 'step down' PCR to attain the full length mildew genomic clones. The single-copy genes, named mpk1 and mpk2, encode putative proteins of 356 and 410 amino acids and carry three and four introns, respectively. Expression studies, using RT-PCR, reveal a differing pattern of tissue gene expression with mpk1 and mpk2 during germling morphogenesis and this is compared with the constitutive expression of the 'control' beta-tubulin gene.

PTK1, a mitogen-activated-protein kinase gene, is required for conidiation, appressorium formation, and pathogenicity of Pyrenophora teres on barley

Mitogen-activated protein kinases (MAPKs) are a group of protein kinases that execute a wide variety of roles in cellular signal transduction pathways such as osmoregulation, cell wall biosynthesis, growth, and differentiation. A polymerase chain reaction (PCR) with degenerate primers based on conserved regions of known MAPKs was used to clone the MAPK gene PTK1 from the leaf pathogen Pyrenophora teres (anamorph Drechslera teres), the causal agent of net blotch of barley (Hordeum vulgare L.). The predicted amino acid sequence shows high homology with MAPKs from other phytopathogenic fungi. The gene is present in the genome as a single copy. PTK1 is expressed during in vitro growth on complete medium, under conidiation-inducing conditions and during infection of barley leaves, as shown by reverse transcription-PCR studies. In order to assess the role of PTK1 in the life cycle of P. teres, targeted gene disruption was conducted. Mutants carrying an interrupted copy of the gene were deficient in conidiation, did not form appressoria on glass surfaces or on barley leaves, lost their ability to infect barley leaves, and could not colonize host tissues following artificial wounding.

Surface attachment and pre-penetration stage development by plant pathogenic fungi

Fungal pathogens cause many of the most serious crop diseases. One of the principal reasons for the success of this group is their ability to locate and perceive appropriate host surfaces and then to elaborate specialized infection structures. Here we review the processes implicated in surface attachment, germ tube elongation, and development of appressoria. The involvement of surface-acting proteins such as fungal hydrophobins and integrins in these processes is evaluated, along with a description of studies that have revealed the existence of conserved signaling pathways that regulate appressorium formation. Finally, we anticipate the prospect of genome-level analysis of fungal pathogens and the key research questions that will need to be addressed.

Map kinases in fungal pathogens

MAP kinases in eukaryotic cells are well known for transducing a variety of extracellular signals to regulate cell growth and differentiation. Recently, MAP kinases homologous to the yeast Fus3/Kss1 MAP kinases have been identified in several fungal pathogens and found to be important for appressorium formation, invasive hyphal growth, and fungal pathogenesis. This MAP kinase pathway also controls diverse growth or differentiation processes, including conidiation, conidial germination, and female fertility. MAP kinases homologous to yeast Slt2 and Hog1 have also been characterized in Candida albicans and Magnaporthe grisea. Mutants disrupted of the Slt2 homologues have weak cell walls, altered hyphal growth, and reduced virulence. The Hog1 homologues are dispensable for growth but are essential for regulating responses to hyperosmotic stress in C. albicans and M. grisea. Overall, recent studies have indicated that MAP kinase pathways may play important roles in regulating growth, differentiation, survival, and pathogenesis in fungal pathogens.

The BMP1 gene is essential for pathogenicity in the gray mold fungus Botrytis cinerea

In Magnaporthe grisea, a well-conserved mitogen-activated protein (MAP) kinase gene, PMK1, is essential for fungal pathogenesis. In this study, we tested whether the same MAP kinase is essential for plant infection in the gray mold fungus Botrytis cinerea, a necrotrophic pathogen that employs infection mechanisms different from those of M. grisea. We used a polymerase chain reaction-based approach to isolate MAP kinase homologues from B. cinerea. The Botrytis MAP kinase required for pathogenesis (BMP) MAP kinase gene is highly homologous to the M. grisea PMK1. BMP1 is a single-copy gene. bmp1 gene replacement mutants produced normal conidia and mycelia but were reduced in growth rate on nutrient-rich medium. bmp1 mutants were nonpathogenic on carnation flowers and tomato leaves. Re-introduction of the wild-type BMP1 allele into the bmp1 mutant restored both normal growth rate and pathogenicity. Further studies indicated that conidia from bmp1 mutants germinated on plant surfaces but failed to penetrate and macerate plant tissues. bmp1 mutants also appeared to be defective in infecting through wounds. These results indicated that BMP1 is essential for plant infection in B. cinerea, and this MAP kinase pathway may be widely conserved in pathogenic fungi for regulating infection processes.

A mitogen-activated protein kinase of the corn leaf pathogen Cochliobolus heterostrophus is involved in conidiation, appressorium formation, and pathogenicity: diverse roles for mitogen-activated protein kinase homologs in foliar pathogens

Fungal pathogens perceive and respond to molecules from the plant, triggering pathogenic development. Transduction of these signals may use heterotrimeric G proteins, and it is thought that protein phosphorylation cascades are also important. We have isolated a mitogen-activated protein kinase homolog from the corn pathogen Cochliobolus heterostrophus to test its role as a component of the transduction pathways. The new gene, CHK1, has a deduced amino acid sequence 90% identical to Pmk1 of the rice blast fungus Magnaporthe grisea and 59% identical to Fus3 of Saccharomyces cerevisiae. A series of chk1 deletion mutants has poorly developed aerial hyphae, autolysis, and no conidia. No pseudothecia are formed when a cross between two Deltachk1 mutants is attempted. The ability of Deltachk1 mutants to infect corn plants is reduced severely. The growth pattern of hyphae on a glass surface is strikingly altered from that of the wild type, forming coils or loops, but no appressoria. This set of phenotypes overlaps only partially with that of pmk1 mutants, the homologous gene of the rice blast fungus. In particular, sexual and asexual sporulation both require Chk1 function in Cochliobolus heterostrophus, in contrast to Pmk1, but perhaps more similar to yeast, where Fus3 transmits the mating signal. Chk1 is required for efficient colonization of leaf tissue, which can be compared with filamentous invasive growth of yeast, modulated through another closely related mitogen-activated protein kinase, Kss1. Ubiquitous signaling elements thus are used in diverse ways in different plant pathogens, perhaps the result of coevolution of the transducers and their targets.

A MAP kinase encoded by the ubc3 gene of Ustilago maydis is required for filamentous growth and full virulence

Ustilago maydis, the causal agent of corn smut disease, displays dimorphic growth in which it alternates between a budding haploid saprophyte and a filamentous dikaryotic pathogen. We are interested in identifying the genetic determinants of filamentous growth and pathogenicity in U. maydis. To do this, we have taken a forward genetic approach. Previously, we showed that haploid adenylate cyclase (uac1) mutants display a constitutively filamentous phenotype. Mutagenesis of a uac1 disruption strain allowed the isolation of a large number of budding suppressor mutants. These mutants are named ubc, for Ustilago bypass of cyclase, as they no longer require the production of cAMP to grow in the budding morphology. Complementation of one of these suppressor mutants led to the identification of ubc3, which is required for filamentous growth and encodes a MAP kinase most similar to those of the yeast pheromone response pathway. In addition to filamentous growth, the ubc3 gene is required for pheromone response and for full virulence. Mutations in the earlier identified fuz7 MAP kinase kinase also suppress the filamentous phenotype of the uac1 disruption mutant, adding evidence that both ubc3 and fuz7 are members of this same MAP kinase cascade. These results support an important interplay of the cAMP and MAP kinase signal transduction pathways in the control of morphogenesis and pathogenicity in U. maydis.

Mitogen-activated protein kinase Mkp1 of Pneumocystis carinii complements the slt2Delta defect in the cell integrity pathway of Saccharomyces cerevisiae

Signal transduction pathways are important in the adaptive response of microbes to their environment. A Pneumocystis carinii extracellular signal-regulated protein kinase (MAPK) homologue, Mkp1, has been isolated by sequence similarity screening of P. carinii genomic DNA. The Mkp1 of P. carinii shows closest homology to other fungal MAP kinases involved in cell integrity signal transduction cascades, including Slt2p/Mpk1p of Saccharomyces cerevisiae, Mkc1 of Candida albicans and Mps1 of Magnaporthe grisea. Defects of Slt2p in S. cerevisiae result in phenotypes of slow growth, and temperature sensitivity in the absence of an osmostabilizer. Overexpression of mkp1 in a strain with the slt2Delta defect fully restored the normal growth rate, and partially reduced lysis at elevated temperatures. Complementation of the slt2Delta defect by Mkp1 demonstrates that Mkp1 is a functional MAP kinase, and that it may be the MAP kinase component of a similar signal transduction cascade within P. carinii. Furthermore, Mkp1 is activated in vitro upon the exposure of P. carinii to conditions of oxidative stress. The investigation of a MAP kinase signal transduction pathway of P. carinii will result in both a better understanding of the mechanism the organism utilizes to respond to environmental changes, and a system to assay responses to these changes.

The alfalfa (Medicago sativa) TDY1 gene encodes a mitogen-activated protein kinase homolog

Development of root nodules, specifically induction of cortical cell division for nodule initiation, requires expression of specific genes in the host and microsymbiont. A full-length cDNA clone and the corresponding genomic clone encoding a MAP (mitogen-activated protein) kinase homolog were isolated from alfalfa (Medicago sativa). The genomic clone, TDY1, encodes a 68.9-kDa protein with 47.7% identity to MMK4, a previously characterized MAP kinase homolog from alfalfa. TDY1 is unique among the known plant MAP kinases, primarily due to a 230 amino acid C-terminal domain. The putative activation motif, Thr-Asp-Tyr (TDY), also differs from the previously reported Thr-Glu-Tyr (TEY) motif in plant MAP kinases. TDY1 messages were found predominantly in root nodules, roots, and root tips. Transgenic alfalfa and Medicago truncatula containing a chimeric gene consisting of 1.8 kbp of 5' flanking sequence of the TDY1 gene fused to the beta-glucuronidase (GUS) coding sequence exhibited GUS expression primarily in the nodule parenchyma, meristem, and vascular bundles, root tips, and root vascular bundles. Stem internodes stained intensely in cortical parenchyma, cambial cells, and primary xylem. GUS activity was observed in leaf mesophyll surrounding areas of mechanical wounding and pathogen invasion. The promoter was also active in root tips and apical meristems of transgenic tobacco. Expression patterns suggest a possible role for TDY1 in initiation and development of nodules and roots, and in localized responses to wounding.

Serine/threonine protein kinases and phosphatases in filamentious fungi

Protein phosphorylation and dephosphorylation are one of the central currencies by which living cells perceive and respond to environmental cues. A number of fundamental processes in fungi such as the cell cycle, transcription, and mating have been shown to require protein phosphorylation. The analysis of protein kinases and phosphatases in filamentous fungi is in its infancy; however, it has already become clear that kinases and phosphatases are likely to be important mediators of fungal proliferation and development as well as signal transduction and infection-related morphogenesis. In this review, we describe, summarize, and consider the rapidly expanding field of protein phosphorylation/dephosphorylation in various aspects of filamentous fungal growth and development.

Mitogen-activated protein kinase: conservation of a three-kinase module from yeast to human

Mitogen-activated protein kinases (MAPK) are serine-threonine protein kinases that are activated by diverse stimuli ranging from cytokines, growth factors, neurotransmitters, hormones, cellular stress, and cell adherence. Mitogen-activated protein kinases are expressed in all eukaryotic cells. The basic assembly of MAPK pathways is a three-component module conserved from yeast to humans. The MAPK module includes three kinases that establish a sequential activation pathway comprising a MAPK kinase kinase (MKKK), MAPK kinase (MKK), and MAPK. Currently, there have been 14 MKKK, 7 MKK, and 12 MAPK identified in mammalian cells. The mammalian MAPK can be subdivided into five families: MAPKerk1/2, MAPKp38, MAPKjnk, MAPKerk3/4, and MAPKerk5. Each MAPK family has distinct biological functions. In Saccharomyces cerevisiae, there are five MAPK pathways involved in mating, cell wall remodelling, nutrient deprivation, and responses to stress stimuli such as osmolarity changes. Component members of the yeast pathways have conserved counterparts in mammalian cells. The number of different MKKK in MAPK modules allows for the diversity of inputs capable of activating MAPK pathways. In this review, we define all known MAPK module kinases from yeast to humans, what is known about their regulation, defined MAPK substrates, and the function of MAPK in cell physiology.

Characterization of a mitogen-activated protein kinase from Pneumocystis carinii

The pathogenic fungus Pneumocystis carinii causes severe pneumonia in patients with impaired immunity, particularly patients with acquired immunodeficiency syndrome. The life cycle of P. carinii is poorly understood, and the inability to continuously culture P. carinii is a major limitation in understanding its cell biology. In fungi homologous to P. carinii, pheromone mating factors signal through a mitogen-activated protein kinase (MAPK) signal transduction cascade, resulting in mitotic cell cycle arrest and entry into a pathway of conjugation, cellular differentiation, and proliferation. Using degenerate PCR and library screening, we have identified a MAPK cDNA in P. carinii that is highly homologous to fungal MAPKs involved in the pheromone mating signal transduction cascade, and we demonstrate MAPK activity in P. carinii lysates with a specific antiserum derived from the translated P. carinii MAPK cDNA sequence.