scholarly journals An Efficient Strategy for Obtaining Mutants by Targeted Gene Deletion in Ophiostoma novo-ulmi

2021 ◽  
Vol 12 ◽  
Author(s):  
Jorge Luis Sarmiento-Villamil ◽  
Thais Campos de Oliveira ◽  
Erika Sayuri Naruzawa ◽  
Louis Bernier
Keyword(s):  
Molecular Mechanisms ◽  
Gene Deletion ◽  
High Efficiency ◽  
Pathogenic Fungi ◽  
Gene Replacement ◽  
Dutch Elm Disease ◽  
Large Set ◽  
Purine Nucleotide ◽  
Dimorphic Fungus ◽  
Dimorphic Fungi

The dimorphic fungus Ophiostoma novo-ulmi is the highly aggressive pathogen responsible for the current, highly destructive, pandemic of Dutch elm disease (DED). Genome and transcriptome analyses of this pathogen previously revealed that a large set of genes expressed during dimorphic transition were also potentially related to plant infection processes, which seem to be regulated by molecular mechanisms different from those described in other dimorphic pathogens. Then, O. novo-ulmi can be used as a representative species to study the lifestyle of dimorphic pathogenic fungi that are not shared by the “model species” Candida albicans and Ustilago maydis. In order to gain better knowledge of molecular aspects underlying infection process and symptom induction by dimorphic fungi that cause vascular wilt disease, we developed a high-throughput gene deletion protocol for O. novo-ulmi. The protocol is based on transforming a Δmus52 O. novo-ulmi mutant impaired for non-homologous end joining (NHEJ) as the recipient strain, and transforming this strain with the latest version of OSCAR plasmids. The latter are used for generating deletion constructs containing the toxin-coding Herpes simplex virus thymidine kinase (HSVtk) gene which prevents ectopic integration of the T-DNA in Ophiostoma DNA. The frequency of gene deletion by homologous recombination (HR) at the ade1 locus associated with purine nucleotide biosynthesis was up to 77.8% in the Δmus52 mutant compared to 2% in the wild-type (WT). To validate the high efficiency of our deletion gene methodology we deleted ade7, which also belongs to the purine nucleotide pathway, as well as bct2, ogf1, and opf2 which encode fungal binuclear transcription factors (TFs). The frequency of gene replacement by HR for these genes reached up to 94%. We expect that our methodology combining the use of NHEJ deficient strains and OSCAR plasmids will function with similar high efficiencies for other O. novo-ulmi genes and other filamentous fungi.

scholarly journals Inoculum Size Effect in Dimorphic Fungi: Extracellular Control of Yeast-Mycelium Dimorphism in Ceratocystis ulmi

2004 ◽  
Vol 70 (3) ◽  
pp. 1356-1359 ◽  
Author(s):  
Jacob M. Hornby ◽  
Sarah M. Jacobitz-Kizzier ◽  
Donna J. McNeel ◽  
Ellen C. Jensen ◽  
David S. Treves ◽  
...  
Keyword(s):  
Quorum Sensing ◽  
Size Effect ◽  
Organic Solvent ◽  
Inoculum Size ◽  
Dutch Elm Disease ◽  
Sulfur Source ◽  
Dimorphic Fungus ◽  
Promoting Effect ◽  
Dimorphic Fungi ◽  
Methyl Donors

ABSTRACT We studied the inoculum size effect in Ceratocystis ulmi, the dimorphic fungus that causes Dutch elm disease. In a defined glucose-proline-salts medium, cells develop as budding yeasts when inoculated at ≥106 spores per ml and as mycelia when inoculated at <106 spores per ml. The inoculum size effect was not influenced by inoculum spore type, age of the spores, temperature, pH, oxygen availability, trace metals, sulfur source, phosphorous source, or the concentration of glucose or proline. Similarly, it was not influenced by added adenosine, reducing agents, methyl donors, amino sugars, fatty acids, or carbon dioxide. Instead, growing cells excreted an unknown quorum-sensing factor that caused a morphological shift from mycelia to budding yeasts. This yeast-promoting effect is abolished if it is extracted with an organic solvent such as ethyl acetate. The quorum-sensing activity acquired by the organic solvent could be added back to fresh medium in a dose-dependent fashion. The quorum-sensing activity in C. ulmi spent medium was specific for C. ulmi and had no effect on the dimorphic fungus Candida albicans or the photomorphogenic fungus Penicillium isariaeforme. In addition, farnesol, the quorum-sensing molecule produced by C. albicans, did not inhibit mycelial development of C. ulmi when present at concentrations of up to 100 μM. We conclude that the inoculum size effect is a manifestation of a quorum-sensing system that is mediated by an excreted extracellular molecule, and we suggest that quorum sensing is a general phenomenon in dimorphic fungi.

Fungi on leaves, branches and stems of trees and shrubs of Saint Petersburg suburban parks

2017 ◽  
Author(s):  
М.В. Сидельникова ◽  
А.В. Тобиас ◽  
Д.Ю. Власов
Keyword(s):  
Pathogenic Fungi ◽  
Dutch Elm Disease ◽  
City Center ◽  
Saint Petersburg ◽  
Xylotrophic Fungi ◽  
Fungi Infection ◽  
Mycological Examination ◽  
The Moment ◽  
Available Information ◽  
Trees And Shrubs

Проведены микологические обследования древесной и кустарниковой растительности на территории парковой зоны Санкт-Петербурга и пригородов. Сбор материала проводился в парках южных пригородов Санкт-Петербурга (Павловский парк, Екатерининский парк, Нижний сад и Верхний парк Ораниенбаума, Верхний сад и Нижний парк ГМЗ «Петергоф»). В сравнительных целях был обследован парк при Обуховской больнице в центре Санкт-Петербурга. На древесно-кустарниковых породах парковой зоны нами выявлено 230 видов грибов (микро- и макромицетов). На листьях выявлено 28 видов микромицетов, в числе которых возбудители мучнистой росы, ржавчины и пятнистостей. На ветвях и стволах древесных пород выявлено 150 видов микромицетов, среди которых есть как часто встречающиеся, так и редкие виды грибов. Большинство из них обнаруживается в анаморфной стадии. Наибольшее разнообразие и развитие микромицетов отмечено на сухих ветвях. Высокой вредоносностью характеризуются тиростромоз липы и голландская болезнь вязов. Выявлены устойчивые патогенные комплексы грибов, развитие которых приводит к заметному ухудшению состояния растений. На стволах живых и усыхающих деревьев, а также растительных остатках отмечено 52 вида макромицетов. Среди них выявлены доминирующие и редкие виды. Среди источников заражения древесных растений ксилотрофными грибами выделяются отмершие вязы, усохшие стволы которых можно наблюдать как в пригородных парках, так и в центральной части Санкт-Петербурга. Полученные данные существенно расширяют имеющиеся сведения по микобиоте парков Санкт-Петербурга. Mycological examination of tree and shrub vegetation on the territory of Saint Petersburg park zone and its suburbs was conducted. Material was collected in the parks of southern suburbs of Saint Petersburg (Pavlovsk Park, Catherine Park, Lower Garden and Upper Park in Oranienbaum, Upper Garden and Lower Park in Peterhof). For comparative purposes Park of Obukhov Hospital in Saint Petersburg city center was also examined. At the moment, 230 fungi species (micro- and macrofungi) were identified on trees and shrubs of the park zone. Among them, 28 species of microfungi, including powdery mildew, rust and blights pathogens were found on leaves. Also, 150 species of microfungi, including both common and rare fungi species, were found on branches and trunks. Most of them were found in the anamorphic stage. The greatest diversity and microfungi development were noted on dry branches. Thyrostromose of linden and Dutch elm disease are the most harmful. Stable complexes of pathogenic fungi, which development leads to clear decline of plants' condition, were identified. In addition, 52 species of macrofungi, including dominant and rare species, were observed on trunks of living and drying trees and vegetation residues. Among the sources of xylotrophic fungi infection of woody plants, dead elms are the most distinguished. Their dead trunks can be found in both suburban parks and the central part of Saint Petersburg. The presented data significantly expand available information on mycobiota Saint Petersburg parks.

scholarly journals Analysis of the Role of Bradysiaimpatiens (Diptera: Sciaridae) as a Vector Transmitting Peanut Stunt Virus on the Model Plant Nicotiana benthamiana

Cells ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1546
Author(s):  
Marta Budziszewska ◽  
Patryk Frąckowiak ◽  
Aleksandra Obrępalska-Stęplowska
Keyword(s):  
Nicotiana Benthamiana ◽  
Molecular Mechanisms ◽  
Virus Transmission ◽  
Pathogenic Fungi ◽  
Economic Losses ◽  
Fungus Gnats ◽  
Droplet Pcr ◽  
Viral Coat ◽  
Peanut Stunt Virus

Bradysia species, commonly known as fungus gnats, are ubiquitous in greenhouses, nurseries of horticultural plants, and commercial mushroom houses, causing significant economic losses. Moreover, the insects from the Bradysia genus have a well-documented role in plant pathogenic fungi transmission. Here, a study on the potential of Bradysia impatiens to acquire and transmit the peanut stunt virus (PSV) from plant to plant was undertaken. Four-day-old larvae of B. impatiens were exposed to PSV-P strain by feeding on virus-infected leaves of Nicotiana benthamiana and then transferred to healthy plants in laboratory conditions. Using the reverse transcription-polymerase chain reaction (RT-PCR), real-time PCR (RT-qPCR), and digital droplet PCR (RT-ddPCR), the PSV RNAs in the larva, pupa, and imago of B. impatiens were detected and quantified. The presence of PSV genomic RNA strands as well as viral coat protein in N. benthamiana, on which the viruliferous larvae were feeding, was also confirmed at the molecular level, even though the characteristic symptoms of PSV infection were not observed. The results have shown that larvae of B. impatiens could acquire the virus and transmit it to healthy plants. Moreover, it has been proven that PSV might persist in the insect body transstadially. Although the molecular mechanisms of virion acquisition and retention during insect development need further studies, this is the first report on B. impatiens playing a potential role in plant virus transmission.

Abstract 126: High Efficiency Reprogramming of Fibroblasts Into Cardiomyocytes Requires Suppression of Pro-fibrotic Signaling

2015 ◽  
Vol 117 (suppl_1) ◽  
Author(s):  
Kunhua Song ◽  
Yuanbiao Zhao ◽  
Pilar Londono ◽  
Emily Sharpe ◽  
Joshua R Clair ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
High Efficiency ◽  
Transforming Growth Factor ◽  
Cardiac Fibroblasts ◽  
Rho Kinase ◽  
Transforming Growth Factor Β ◽  
Direct Reprogramming ◽  
Cardiac Gene Expression ◽  
Cardiac Gene ◽  
Kinetics Of

The mammalian heart is composed of ~30% cardiomyocytes which have limited capacity to regenerate and ~70% non-cardiomyocytes including endothelial cells and cardiac fibroblasts. Direct reprogramming of fibroblasts into cardiomyocytes by forced expression of cardiomyogenic transcription factors, GMT (GATA4, Mef2C, Tbx5) or GHMT (GATA4, Hand2, Mef2C, Tbx5), has recently been demonstrated, suggesting a novel therapeutic strategy for cardiac repair. Despite extensive efforts, the efficiency of direct reprogramming of embryonic or adult fibroblasts into cardiomyocytes has yet to exceed 20%, or 0.1% respectively, leading many in the field to question the clinical translatability of this method. Here, we demonstrate that pro-fibrotic signaling events governed by transforming growth factor-β (TGF-β) and Rho kinase (ROCK) are concomitantly activated in GHMT-expressing fibroblasts, leading to potent suppression of cardiac reprogramming ( Figure 1 ). Remarkably, pharmacological inhibition of TGF-β, or ROCK leads to conversion of ≥ 60% of fibroblasts into highly functional cardiomyocytes, displaying global cardiac gene expression, spontaneous contractility, action potentials and calcium transients. Furthermore, inhibition of TGF-β, or ROCK dramatically enhances the kinetics of cardiac reprogramming, with spontaneously contracting cardiomyocytes emerging in less than two weeks, as opposed to 4 weeks with GHMT alone. These findings provide new insights into the molecular mechanisms underlying cardiac conversion of fibroblasts, and should enhance efforts to generate cardiomyocytes for clinical applications.

scholarly journals 641 Spatially organized multicellular immune hubs in MMRd and MMRp colorectal cancer

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A670-A670
Author(s):  
Jonathan Chen ◽  
Karin Pelka ◽  
Matan Hofree ◽  
Marios Giannakis ◽  
Genevieve Boland ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
T Cells ◽  
T Cell ◽  
Immune Responses ◽  
Mismatch Repair ◽  
Molecular Mechanisms ◽  
Immune Cell ◽  
Single Cells ◽  
Large Set ◽  
Colon Tissue

BackgroundImmune responses to cancer are highly variable, with DNA mismatch repair-deficient (MMRd) tumors exhibiting more anti-tumor immunity than mismatch repair-proficient (MMRp) tumors. Almost all tumors are infiltrated with immune cells, but the types of immune responses and their effects on tumor growth, metastasis and death, vary greatly between different cancers and individual tumors. Which of the numerous cell subsets in a tumor contribute to the response, how their interactions are regulated, and how they are spatially organized within tumors remains poorly understood.MethodsTo understand the rules governing these varied responses, we transcriptionally profiled 371,223 single cells from colorectal tumors and adjacent normal tissues of 28 MMRp and 34 MMRd treatment-naive patients. We developed a systematic approach to discover cell types, their underlying gene programs, and cellular communities based on single cell RNA-seq (scRNAseq) profiles and applied it to study the distinguishing features of human MMRd and MMRp colorectal cancer. Cellular communities discovered from this analysis were spatially mapped in tissue sections using multiplex RNA in situ hybridization microscopy.ResultsTo understand the basis for differential immune responses in CRC, we first determined and compared the immune cell composition of MMRd and MMRp CRC and normal colon tissue, finding dramatic remodeling between tumor and normal tissue and between MMRd and MMRp tumors, particularly within the myeloid, T cell, and stromal compartments. Among the clusters enriched in MMRd tumors were activated CXCL13+ CD8 T cells. Importantly, gene program co-variation analysis revealed multicellular networks. We discovered a myeloid cell-attracting hub at the tumor-luminal interface associated with tissue damage, and an MMRd-enriched immune hub within the tumor, with activated IFNG+ and CXCL13+ T cells together with malignant and myeloid cells expressing T-cell-attracting chemokines (figure 1).ConclusionsOur study provides a rich dataset of cellular states, gene programs and their transformations in tumors across a relatively large cohort of patients with colorectal cancer. Our predictions of several multicellular hubs based on co-variation of gene expression programs, and subsequent spatial localization of two major immune-malignant hubs, organizes a large set of cell states and programs into a smaller number of coordinated networks of cells and processes. Understanding the molecular mechanisms underlying these hubs, and studying their temporal and spatial regulation upon treatment will be critical for advancing cancer therapy.Ethics ApprovalThis study was approved by the DF-HCC institutional review board (protocols 03-189 and 02-240).Abstract 641 Figure 1A coordinated network of CXCL13+ T cells with myeloid and malignant cells expressing ISGs. Image shows a portion of formalin-fixed paraffin-embedded tissue from an MMRd CRC specimen stained with multiplex RNA ISH / IF for PanCK-IF, CD3E-ISH, CXCL10/CXCL11-ISH, CXCL13-ISH, and IFNG-ISH. Note IFNG+ and CXCL13+ cells in proximity to cells expressing the chemokines CXCL10/CXCL11

scholarly journals Activation of the complement system by pathogenic fungi.

1996 ◽  
Vol 9 (1) ◽  
pp. 34-46 ◽  
Author(s):  
T R Kozel
Keyword(s):  
Complement System ◽  
Host Resistance ◽  
Molecular Mechanisms ◽  
Fungal Infections ◽  
Pathogenic Fungi ◽  
Complement Cascade ◽  
Experimental Animals ◽  
Molecular Bases ◽  
The Complement System

Fungi have been studied as prototype activators of the complement cascade since the early 1900s. More recently, attention has focused on the role of the complement system in the pathogenesis of fungal infections. The interactions of Cryptococcus neoformans and Candida albicans with the complement system are the most widely characterized; however, all pathogenic fungi examined to date have the ability to initiate the complement cascade. The molecular mechanisms for initiation and regulation of the complement cascade differ from one fungus to another, most likely reflecting differences in the structure of the outer layers of the cell wall. The molecular bases for such differences remain to be identified. Studies of mycoses in experimental animals with induced or congenital deficiencies in the complement system demonstrate that complement is an important innate system for control of fungal infection. Contributions to host resistance include opsonization and generation of inflammatory mediators. Inflammation induced by chemotactic products of the complement system may contribute to the pathogenesis of some fungal infections.

scholarly journals Primary and Secondary Metabolic Effects of a Key Gene Deletion (ΔYPL062W) in Metabolically Engineered Terpenoid-ProducingSaccharomyces cerevisiae

2019 ◽  
Vol 85 (7) ◽  
Author(s):  
Yan Chen ◽  
Ying Wang ◽  
Ming Liu ◽  
Junze Qu ◽  
Mingdong Yao ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Gene Deletion ◽  
Core Promoter ◽  
Strain Improvement ◽  
Genetic Alterations ◽  
Metabolic Effects ◽  
Industrial Biotechnology ◽  
Cell Factory ◽  
Content Type ◽  
Genetic Function

ABSTRACTSaccharomyces cerevisiaeis an established cell factory for production of terpenoid pharmaceuticals and chemicals. Numerous studies have demonstrated that deletion or overexpression of off-pathway genes in yeast can improve terpenoid production. The deletion ofYPL062WinS. cerevisiae, in particular, has benefitted carotenoid production by channeling carbon toward carotenoid precursors acetyl coenzyme A (acetyl-CoA) and mevalonate. The genetic function ofYPL062Wand the molecular mechanisms for these benefits are unknown. In this study, we systematically examined this gene deletion to uncover the gene function and its molecular mechanism. RNA sequencing (RNA-seq) analysis uncovered thatYPL062Wdeletion upregulated the pyruvate dehydrogenase bypass, the mevalonate pathway, heterologous expression of galactose (GAL) promoter-regulated genes, energy metabolism, and membrane composition synthesis. Bioinformatics analysis and serial promoter deletion assay revealed thatYPL062Wfunctions as a core promoter forALD6and that the expression level ofALD6is negatively correlated to terpenoid productivity. We demonstrate that ΔYPL062Wincreases the production of all major terpenoid classes (C10, C15, C20, C30, and C40). Our study not only elucidated the biological function ofYPL062Wbut also provided a detailed methodology for understanding the mechanistic aspects of strain improvement.IMPORTANCEAlthough computational and reverse metabolic engineering approaches often lead to improved gene deletion mutants for cell factory engineering, the systems level effects of such gene deletions on the production phenotypes have not been extensively studied. Understanding the genetic and molecular function of such gene alterations on production strains will minimize the risk inherent in the development of large-scale fermentation processes, which is a daunting challenge in the field of industrial biotechnology. Therefore, we established a detailed experimental and systems biology approach to uncover the molecular mechanisms ofYPL062Wdeletion inS. cerevisiae, which is shown to improve the production of all terpenoid classes. This study redefines the genetic function ofYPL062W, demonstrates a strong correlation betweenYPL062Wand terpenoid production, and provides a useful modification for the creation of terpenoid production platform strains. Further, this study underscores the benefits of detailed and systematic characterization of the metabolic effects of genetic alterations on engineered biosynthetic factories.

scholarly journals Organization and Evolutionary Trajectory of the Mating Type (MAT) Locus in Dermatophyte and Dimorphic Fungal Pathogens

2009 ◽  
Vol 9 (1) ◽  
pp. 46-58 ◽  
Author(s):  
Wenjun Li ◽  
Banu Metin ◽  
Theodore C. White ◽  
Joseph Heitman
Keyword(s):  
Mating Type ◽  
Fungal Pathogens ◽  
Control Cell ◽  
Gene Arrangement ◽  
Microsporum Canis ◽  
Microsporum Gypseum ◽  
Last Common Ancestor ◽  
Dimorphic Fungus ◽  
Dimorphic Fungi ◽  
Evolutionary Trajectory

ABSTRACT Sexual reproduction in fungi is governed by a specialized genomic region, the mating type (MAT) locus, whose gene identity, organization, and complexity are diverse. We identified the MAT locus of five dermatophyte fungal pathogens (Microsporum gypseum, Microsporum canis, Trichophyton equinum, Trichophyton rubrum, and Trichophyton tonsurans) and a dimorphic fungus, Paracoccidioides brasiliensis, and performed phylogenetic analyses. The identified MAT locus idiomorphs of M. gypseum control cell type identity in mating assays, and recombinant progeny were produced. Virulence tests in Galleria mellonella larvae suggest the two mating types of M. gypseum may have equivalent virulence. Synteny analysis revealed common features of the MAT locus shared among these five dermatophytes: namely, a small size (∼3 kb) and a novel gene arrangement. The SLA2, COX13, and APN2 genes, which flank the MAT locus in other Ascomycota are instead linked on one side of the dermatophyte MAT locus. In addition, the transcriptional orientations of the APN2 and COX13 genes are reversed compared to the dimorphic fungi Histoplasma capsulatum, Coccidioides immitis, and Coccidioides posadasii. A putative transposable element, pogo, was found to have inserted in the MAT1-2 idiomorph of one P. brasiliensis strain but not others. In conclusion, the evolution of the MAT locus of the dermatophytes and dimorphic fungi from the last common ancestor has been punctuated by both gene acquisition and expansion, and asymmetric gene loss. These studies further support a foundation to develop molecular and genetic tools for dermatophyte and dimorphic human fungal pathogens.

scholarly journals Fungal Functional Genomics: Tunable Knockout-Knock-in Expression and Tagging Strategies

2009 ◽  
Vol 8 (5) ◽  
pp. 800-804 ◽  
Author(s):  
Luis F. Larrondo ◽  
Hildur V. Colot ◽  
Christopher L. Baker ◽  
Jennifer J. Loros ◽  
Jay C. Dunlap
Keyword(s):  
Functional Genomics ◽  
Target Gene ◽  
High Efficiency ◽  
Expression System ◽  
Gene Replacement ◽  
Fungal Species ◽  
Homologous Gene ◽  
Molecular Tools ◽  
Phenotypic Information ◽  
Endogenous Loci

ABSTRACT Strategies for promoting high-efficiency homologous gene replacement have been developed and adopted for many filamentous fungal species. The next generation of analysis requires the ability to manipulate gene expression and to tag genes expressed from their endogenous loci. Here we present a suite of molecular tools that provide versatile solutions for fungal high-throughput functional genomics studies based on locus-specific modification of any target gene. Additionally, case studies illustrate caveats to presumed overexpression constructs. A tunable expression system and different tagging strategies can provide valuable phenotypic information for uncharacterized genes and facilitate the analysis of essential loci, an emerging problem in systematic deletion studies of haploid organisms.

scholarly journals An ste20 Homologue in Ustilago maydis Plays a Role in Mating and Pathogenicity

2004 ◽  
Vol 3 (1) ◽  
pp. 180-189 ◽  
Author(s):  
David G. Smith ◽  
Maria D. Garcia-Pedrajas ◽  
Wei Hong ◽  
Zhanyang Yu ◽  
Scott E. Gold ◽  
...  
Keyword(s):  
Protein Kinase ◽  
Plant Pathogen ◽  
Genomic Library ◽  
Pathogenic Fungi ◽  
Ustilago Maydis ◽  
Kinase Domain ◽  
Mapk Cascade ◽  
Mitogen Activated Protein Kinase ◽  
Dimorphic Fungi ◽  
Mitogen Activated Protein

ABSTRACT The mitogen-activated protein kinase (MAPK) pathways are conserved from fungi to humans and have been shown to play important roles in mating and filamentous growth for both Saccharomyces cerevisiae and dimorphic fungi and in infectivity for pathogenic fungi. STE20 encodes a protein kinase of the p21-activated protein kinase family that regulates more than one of these cascades in yeasts. We hypothesized that an Ste20p homologue would play a similar role in the dimorphic plant pathogen Ustilago maydis. The full-length copy of the U. maydis gene was obtained from a genomic library; it lacked introns and was predicted to encode a protein of 826 amino acids, whose sequence confirmed its identity as the first Ste20p homologue to be isolated from a plant pathogen. The predicted protein contained both an N-terminal regulatory Cdc42-Rac interactive binding domain and a C-terminal catalytic kinase domain. Disruption of the gene smu1 resulted in a delayed mating response in a mating-type-specific manner and also in a severe reduction in disease production on maize. Unlike the Ustilago bypass of cyclase (ubc) mutations previously identified in genes in the pheromone-responsive MAPK cascade, mutation of smu1 does not by itself act as an extragenic suppressor of the filamentous phenotype of a uac1 mutant. Thus, the direct connection of Smu1p to MAPK cascade function has yet to be established. Even so, Smu1, though not absolutely required for mating, is necessary for wild-type mating and pathogenicity.

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