[Show abstract][Hide abstract] ABSTRACT: Mendel laws of inheritance can be cheated by Meiotic Drive Elements (MDs), complex nuclear genetic loci found in various eukaryotic genomes and distorting segregation in their favor. Here, we identify and characterize in the model fungus Podospora anserina Spok1 and Spok2, two MDs known as Spore Killers. We show that they are related genes with both spore-killing distorter and spore-protecting responder activities carried out by the same allele. These alleles act as autonomous elements, exert their effects independently of their location in the genome and can act as MDs in other fungi. Additionally, Spok1 acts as a resistance factor to Spok2 killing. Genetical data and cytological analysis of Spok1 and Spok2 localization during the killing process suggest a complex mode of action for Spok proteins. Spok1 and Spok2 belong to a multigene family prevalent in the genomes of many ascomycetes. As they have no obvious cellular role, Spok1 and Spok2 Spore Killer genes represent a novel kind of selfish genetic elements prevalent in fungal genome that proliferate through meiotic distortion.
[Show abstract][Hide abstract] ABSTRACT: While the extent and impact of horizontal transfers in prokaryotes are widely acknowledged, their importance to the eukaryotic kingdom is unclear and thought by many to be anecdotal. Here we report multiple recent transfers of a huge genomic island between Penicillium spp. found in the food environment. Sequencing of the two leading filamentous fungi used in cheese making, P. roqueforti and P. camemberti, and comparison with the penicillin producer P. rubens reveals a 575 kb long genomic island in P. roqueforti-called Wallaby-present as identical fragments at non-homologous loci in P. camemberti and P. rubens. Wallaby is detected in Penicillium collections exclusively in strains from food environments. Wallaby encompasses about 250 predicted genes, some of which are probably involved in competition with microorganisms. The occurrence of multiple recent eukaryotic transfers in the food environment provides strong evidence for the importance of this understudied and probably underestimated phenomenon in eukaryotes.
[Show abstract][Hide abstract] ABSTRACT: In the model fungus Podospora anserina, the PaYIP3 gene encoding the orthologue of the Saccharomyces cerevisiae YIP3 Rab-GDI complex dissociation factor expresses two polypeptides, one of which, the long form, is produced through a programmed translation frameshift. Inactivation of PaYIP3 results in slightly delayed growth associated with modification in repartition of fruiting body on the thallus, along with reduced ascospore production on wood. Long and short forms of PaYIP3 are expressed in the mycelium, while only the short form appears expressed in the maturing fruiting body (perithecium). The frameshift has been conserved over the evolution of the Pezizomycotina, lasting for over 400 million years, suggesting that it has an important role in the wild.
PLoS ONE 01/2013; 8(9):e73772. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we report the construction of two plasmids designed to target DNA sequences to two specific loci of Podospora anserina. Because, in filamentous fungi, integration of transgenes proceeds mainly through non-homologous recombination, transformation results in a random distribution of these DNA sequences. Moreover, they are often found as multiple copies clustered at a single locus. Therefore, for a given transgene, expression may be highly variable among independent transformants. To get rid of both multiple copies and position effects, due to the impact of the chromatin structure upon transgene expression, we constructed tools to specifically target single copies at two well-defined loci, Pa_2_3690 and Pa_4_5450 (Espagne et al., 2008). These genes have been chosen for the following reasons: (1) they have a relatively stable expression during the entire Podospora's life cycle, (2) complete deletion of their ORF does not lead to an abnormal phenotype (Bidard et al., 2011), (3) they are located on two different chromosomes and (4) their second division segregation (SDS) frequency is 80% and 90%, respectively. Besides, a highly efficient homologous recombination ΔPaKu70 strain is available (El-Khoury et al., 2008), which makes gene replacement fairly easy. Taking advantage of this strain, we designed two plasmid tools to target genomic integration of any DNA fragment.
[Show abstract][Hide abstract] ABSTRACT: The Podospora anserina PaMpk1 MAP kinase (MAPK) signaling pathway can generate a cytoplasmic and infectious element resembling prions. When present in the cells, this C element causes the crippled growth (CG) cell degeneration. CG results from the inappropriate autocatalytic activation of the PaMpk1 MAPK pathway during growth, whereas this cascade normally signals stationary phase. Little is known about the control of such prion-like hereditary units involved in regulatory inheritance. Here, we show that another MAPK pathway, PaMpk2, is crucial at every stage of the fungus life cycle, in particular those controlled by PaMpk1 during stationary phase, which includes the generation of C. Inactivation of the third P. anserina MAPK pathway, PaMpk3, has no effect on the development of the fungus. Mutants of MAPK, MAPK kinase, and MAPK kinase kinase of the PaMpk2 pathway are unable to present CG. This inability likely relies upon an incorrect activation of PaMpk1, although this MAPK is normally phosphorylated in the mutants. In PaMpk2 null mutants, hyphae are abnormal and PaMpk1 is mislocalized. Correspondingly, stationary phase differentiations controlled by PaMpk1 are defective in the mutants of the PaMpk2 cascade. Constitutive activation of the PaMpk2 pathway mimics in many ways its inactivation, including an effect on PaMpk1 localization. Analysis of double and triple mutants inactivated for two or all three MAPK genes undercover new growth and differentiation phenotypes, suggesting overlapping roles. Our data underscore the complex regulation of a prion-like element in a model organism.
[Show abstract][Hide abstract] ABSTRACT: Although most eukaryotes reproduce sexually at some moment of their life cycle, as much as a fifth of fungal species were thought to reproduce exclusively asexually. Nevertheless, recent studies have revealed the occurrence of sex in some of these supposedly asexual species. For industrially relevant fungi, for which inoculums are produced by clonal-subcultures since decades, the potentiality for sex is of great interest for strain improvement strategies. Here, we investigated the sexual capability of the fungus Penicillium roqueforti, used as starter for blue cheese production. We present indirect evidence suggesting that recombination could be occurring in this species. The screening of a large sample of strains isolated from diverse substrates throughout the world revealed the existence of individuals of both mating types, even in the very same cheese. The MAT genes, involved in fungal sexual compatibility, appeared to evolve under purifying selection, suggesting that they are still functional. The examination of the recently sequenced genome of the FM 164 cheese strain enabled the identification of the most important genes known to be involved in meiosis, which were found to be highly conserved. Linkage disequilibria were not significant among three of the six marker pairs and 11 out of the 16 possible allelic combinations were found in the dataset. Finally, the detection of signatures of repeat induced point mutations (RIP) in repeated sequences and transposable elements reinforces the conclusion that P. roqueforti underwent more or less recent sex events. In this species of high industrial importance, the induction of a sexual cycle would open the possibility of generating new genotypes that would be extremely useful to diversify cheese products.
PLoS ONE 01/2012; 7(11):e49665. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We identify a large coiled-coil protein, Sme4/PaMe4, that is highly conserved among the large group of Sordariales and plays central roles in two temporally and functionally distinct aspects of the fungal sexual cycle: first as a component of the meiotic synaptonemal complex (SC) and then, after disappearing and reappearing, as a component of the spindle pole body (SPB). In both cases, the protein mediates spatial juxtaposition of two major structures: linkage of homolog axes through the SC and a change in the SPB from a planar to a bent conformation. Corresponding mutants exhibit defects, respectively, in SC and SPB morphogenesis, with downstream consequences for recombination and astral-microtubule nucleation plus postmeiotic nuclear migration. Sme4 is also required for reorganization of recombination complexes in which Rad51, Mer3, and Msh4 foci relocalize from an on-axis position to a between-axis (on-SC) position concomitant with SC installation. Because involved recombinosome foci represent total recombinational interactions, these dynamics are irrespective of their designation for maturation into cross-overs or noncross-overs. The defined dual roles for Sme4 in two different structures that function at distinct phases of the sexual cycle also provide more functional links and evolutionary dynamics among the nuclear envelope, SPB, and SC.
Proceedings of the National Academy of Sciences 06/2011; 108(26):10614-9. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NADPH oxidases are enzymes that produce reactive oxygen species. Studies in mammals, plants and fungi have shown that they play important roles in differentiation, defence, host/pathogen interaction and mutualistic symbiosis. In this paper, we have identified a Podospora anserina mutant strain impaired for processes controlled by PaNox1 and PaNox2, the two Nox isoforms characterized in this model ascomycete. We show that the gene mutated is PaNoxR, the homologue of the gene encoding the regulatory subunit p67(phox), conserved in mammals and fungi, and that PaNoxR regulates both PaNox1 and PaNox2. Genome sequence analysis of P. anserina reveals that this fungus posses a third Nox isoform, PaNox3, related to human Nox5/Duox and plant Rboh. We have generated a knock-out mutant of PaNox3 and report that PaNox3 plays a minor role in P. anserina, if any. We show that PaNox1 and PaNox2 play antagonist roles in cellulose degradation. Finally, we report for the first time that a saprobic fungus, P. anserina, develops special cell structures dedicated to breach and to exploit a solid cellulosic substrate, cellophane. Importantly, as for similar structures present in some plant pathogens, their proper differentiation requires PaNox1, PaNox2, PaNoxR and the tetraspanin PaPls1.
[Show abstract][Hide abstract] ABSTRACT: Aromatic amines (AA) are a major class of environmental pollutants that have been shown to have genotoxic and cytotoxic potentials toward most living organisms. Fungi are able to tolerate a diverse range of chemical compounds including certain AA and have long been used as models to understand general biological processes. Deciphering the mechanisms underlying this tolerance may improve our understanding of the adaptation of organisms to stressful environments and pave the way for novel pharmaceutical and/or biotechnological applications. We have identified and characterized two arylamine N-acetyltransferase (NAT) enzymes (PaNAT1 and PaNAT2) from the model fungus Podospora anserina that acetylate a wide range of AA. Targeted gene disruption experiments revealed that PaNAT2 was required for the growth and survival of the fungus in the presence of toxic AA. Functional studies using the knock-out strains and chemically acetylated AA indicated that tolerance of P. anserina to toxic AA was due to the N-acetylation of these chemicals by PaNAT2. Moreover, we provide proof-of-concept remediation experiments where P. anserina, through its PaNAT2 enzyme, is able to detoxify the highly toxic pesticide residue 3,4-dichloroaniline in experimentally contaminated soil samples. Overall, our data show that a single xenobiotic-metabolizing enzyme can mediate tolerance to a major class of pollutants in a eukaryotic species. These findings expand the understanding of the role of xenobiotic-metabolizing enzyme and in particular of NATs in the adaptation of organisms to their chemical environment and provide a basis for new systems for the bioremediation of contaminated soils.
Journal of Biological Chemistry 06/2009; 284(28):18726-33. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Convergent evolution of trophic life style and morphological characters are very common in the fungal kingdom. Recently, we have shown that the same molecular machinery containing a tetraspanin and a NADPH oxidase has been recruited in two different fungal species for the same purpose (exiting from a melanized re-enforced cell at a focal weakened point), but at different stages of their development (ascospore germination and appressorium mediated penetration). Although this molecular machinery is required at these key developmental steps, it is also likely involved in specialized cellular functions at other stages of fungal development, as shown here for nutrient acquisition by Podospora anserina.
[Show abstract][Hide abstract] ABSTRACT: Pls1 tetraspanins were shown for some pathogenic fungi to be essential for appressorium-mediated penetration into their host plants. We show here that Podospora anserina, a saprobic fungus lacking appressorium, contains PaPls1, a gene orthologous to known PLS1 genes. Inactivation of PaPls1 demonstrates that this gene is specifically required for the germination of ascospores in P. anserina. These ascospores are heavily melanized cells that germinate under inducing conditions through a specific pore. On the contrary, MgPLS1, which fully complements a DeltaPaPls1 ascospore germination defect, has no role in the germination of Magnaporthe grisea nonmelanized ascospores but is required for the formation of the penetration peg at the pore of its melanized appressorium. P. anserina mutants with mutation of PaNox2, which encodes the NADPH oxidase of the NOX2 family, display the same ascospore-specific germination defect as the DeltaPaPls1 mutant. Both mutant phenotypes are suppressed by the inhibition of melanin biosynthesis, suggesting that they are involved in the same cellular process required for the germination of P. anserina melanized ascospores. The analysis of the distribution of PLS1 and NOX2 genes in fungal genomes shows that they are either both present or both absent. These results indicate that the germination of P. anserina ascospores and the formation of the M. grisea appressorium penetration peg use the same molecular machinery that includes Pls1 and Nox2. This machinery is specifically required for the emergence of polarized hyphae from reinforced structures such as appressoria and ascospores. Its recurrent recruitment during fungal evolution may account for some of the morphogenetic convergence observed in fungi.
[Show abstract][Hide abstract] ABSTRACT: The dung-inhabiting ascomycete fungus Podospora anserina is a model used to study various aspects of eukaryotic and fungal biology, such as ageing, prions and sexual development.
We present a 10X draft sequence of P. anserina genome, linked to the sequences of a large expressed sequence tag collection. Similar to higher eukaryotes, the P. anserina transcription/splicing machinery generates numerous non-conventional transcripts. Comparison of the P. anserina genome and orthologous gene set with the one of its close relatives, Neurospora crassa, shows that synteny is poorly conserved, the main result of evolution being gene shuffling in the same chromosome. The P. anserina genome contains fewer repeated sequences and has evolved new genes by duplication since its separation from N. crassa, despite the presence of the repeat induced point mutation mechanism that mutates duplicated sequences. We also provide evidence that frequent gene loss took place in the lineages leading to P. anserina and N. crassa. P. anserina contains a large and highly specialized set of genes involved in utilization of natural carbon sources commonly found in its natural biotope. It includes genes potentially involved in lignin degradation and efficient cellulose breakdown.
The features of the P. anserina genome indicate a highly dynamic evolution since the divergence of P. anserina and N. crassa, leading to the ability of the former to use specific complex carbon sources that match its needs in its natural biotope.
[Show abstract][Hide abstract] ABSTRACT: In various organisms, thioredoxins are known to be involved in the reduction of protein disulfide bonds and in protecting the cell from oxidative stress. Genes encoding thioredoxins were found by searching the complete genome sequence of the filamentous ascomycete Podospora anserina. Among them, PaTrx1, PaTrx2, and PaTrx3 are predicted to be canonical cytosolic proteins without additional domains. Targeted disruption of PaTrx1, PaTrx2, and PaTrx3 shows that PaTrx1 is the major thioredoxin involved in sulfur metabolism. Deletions have no effect on peroxide resistance; however, data show that either PaTrx1 or PaTrx3 is necessary for sexual reproduction and for the development of the crippled growth cell degeneration (CG), processes that also required the PaMpk1 mitogen-activated protein kinase (MAPK) pathway. Since PaTrx1 PaTrx3 mutants show not an enhancement but rather an impairment in CG, it seems unlikely that PaTrx1 and PaTrx3 thioredoxins participate in the inhibition of this MAPK pathway. Altogether, these results underscore a role for thioredoxins in fungal development.
[Show abstract][Hide abstract] ABSTRACT: Recent research using fungi as models provide new insight into the ability of regulatory networks to generate cellular states that are sufficiently stable to be faithfully transmitted to daughter cells, thereby generating epigenetic inheritance. Such protein-based inheritance is driven by infectious factors endowed with properties usually displayed by prions. We emphasize the contribution of regulatory networks to the emerging properties displayed by cells.
[Show abstract][Hide abstract] ABSTRACT: Filamentous fungi frequently present degenerative processes, whose molecular basis is very often unknown. Here, we present three mutant screens that result in the identification of 29 genes that directly or indirectly control Crippled Growth (CG), an epigenetic cell degeneration of the filamentous ascomycete Podospora anserina. Two of these genes were previously shown to encode a MAP kinase kinase kinase and an NADPH oxidase involved in a signal transduction cascade that participates in stationary phase differentiations, fruiting body development and defence against fungal competitors. The numerous genes identified can be incorporated in a model in which CG results from the sustained activation of the MAP kinase cascade. Our data also emphasize the complex regulatory network underlying three interconnected processes in P. anserina: sexual reproduction, defence against competitors, and cell degeneration.
Fungal Genetics and Biology 07/2005; 42(6):564-77. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NADPH oxidases are enzymes that produce reactive oxygen species (ROS) using electrons derived from intracellular NADPH. In plants and mammals, ROS have been proposed to be second messengers that signal defence responses or cell proliferation. By inactivating PaNox1 and PaNox2, two genes encoding NADPH oxidases, we demonstrate the crucial role of these enzymes in the control of two key steps of the filamentous fungus Podospora anserina life cycle. PaNox1 mutants are impaired in the differentiation of fruiting bodies from their progenitor cells, and the deletion of the PaNox2 gene specifically blocks ascospore germination. Furthermore, we show that PaNox1 likely acts upstream of PaASK1, a MAPKKK previously implicated in stationary phase differentiation and cell degeneration. Using nitro blue tetrazolium (NBT) and diaminobenzidine (DAB) assays, we detect a regulated secretion of both superoxide and peroxide during P. anserina vegetative growth. In addition, two oxidative bursts are shown to occur during fruiting body development and ascospore germination. Analysis of mutants establishes that PaNox1, PaNox2, and PaASK1, as well as a still unknown additional source of ROS, modulate these secretions. Altogether, our data point toward a role for NADPH oxidases in signalling fungal developmental transitions with respect to nutrient availability. These enzymes are conserved in other multicellular eukaryotes, suggesting that early eukaryotes were endowed with a redox network used for signalling purposes.
Fungal Genetics and Biology 12/2004; 41(11):982-97. · 3.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Morphological plasticity is a hallmark of eumycetes. In addition to genes and environment, epigenetic factors control cell, colony and thallus forms in many species, by creating reversible switches. Current knowledge indicates that the different shapes are due to structural or regulatory heritable states of cytoplasmic components. Cellular physiology differs in the various forms, permitting adaptation to fluctuation in the environment. These switches are part of the adaptation repertoire that fungi exhibit to colonize most niches.
Current Opinion in Microbiology 01/2004; 6(6):641-5. · 8.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cytosine methylation is critical for correct development and genome stability in mammals and plants. In order to elucidate the factors that control genomic DNA methylation patterning, a genetic screen for mutations that disrupt methylation-correlated silencing of the endogenous gene PAI2 was conducted in Arabidopsis: This screen yielded seven loss-of-function alleles in a SET domain protein with histone H3 Lys9 methyltransferase activity, SUVH4. The mutations conferred reduced cytosine methylation on PAI2, especially in non-CG sequence contexts, but did not affect methylation on another PAI locus carrying two genes arranged as an inverted repeat. Moreover, an unmethylated PAI2 gene could be methylated de novo in the suvh4 mutant background. These results suggest that SUVH4 is involved in maintenance but not establishment of methylation at particular genomic regions. In contrast, a heterochromatin protein 1 homolog, LHP1, had no effect on PAI methylation.
The EMBO Journal 01/2003; 21(24):6842-52. · 9.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plants maintain cytosine methylation at CG and non-CG residues to control gene expression and genome stability. In a screen for Arabidopsis mutants that alter methylation and silencing of a densely methylated endogenous reporter gene, we recovered 11 loss-of-function alleles in the CMT3 chromomethylase gene. The cmt3 mutants displayed enhanced expression and reduced methylation of the reporter, particularly at non-CG cytosines. CNG methylation was also reduced at repetitive centromeric sequences. Thus, CMT3 is a key determinant for non-CG methylation. The lack of CMT homologs in animal genomes could account for the observation that in contrast to plants, animals maintain primarily CG methylation.
Genes & Development 08/2001; 15(14):1753-8. · 12.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have shown previously that masc1, a gene encoding a putative C5-DNA-methyltransferase (MTase), was necessary for the de novo 'Methylation Induced Premeiotically' (MIP) process and sexual reproduction in Ascobolus, whereas it was dispensable for maintenance methylation. A second MTase gene from Ascobolus, masc2, encodes a protein, Masc2, which possesses the large amino-terminal part characteristic of eukaryotic maintenance MTases. In vitro assays have shown that Masc2 displays a methylation activity, suggesting that it might be the MTase responsible for maintenance methylation. To check its function in vivo, we engineered a disruption of the masc2 gene. The resulting mutant strains did not exhibit any particular phenotype during either vegetative growth or sexual reproduction. Neither the masc2 mutation nor the double masc1 masc2 mutation had any detectable effect upon the maintenance of the pre-existing methylation of single gene copies previously subjected to MIP, natural retroelement-like repeats and tandemly repeated rDNA. The masc2 mutation did not alter either MIP or the other de novo methylation process that operates in vegetatives cells. Nor did it impair the meiotic process of methylation transfer. These results suggest that at least a third MTase gene responsible for maintenance and vegetative de novo methylation is present in Ascobolus.