Genetic variability and chromosome-length polymorphisms of the witches' broom pathogen Crinipellis perniciosa from various plant hosts in South America

Clonal reproduction of Moniliophthora roreri and the emergence of unique lineages with distinct genomes during range expansion

The basidiomycete Moniliophthora roreri causes frosty pod rot of cacao (Theobroma cacao) in the western hemisphere. Moniliophthora roreri is considered asexual and haploid throughout its hemibiotrophic life cycle. To understand the processes driving genome modification, using long-read sequencing technology, we sequenced and assembled 5 high-quality M. roreri genomes out of a collection of 99 isolates collected throughout the pathogen's range. We obtained chromosome-scale assemblies composed of 11 scaffolds. We used short-read technology to sequence the genomes of 22 similarly chosen isolates. Alignments among the 5 reference assemblies revealed inversions, translocations, and duplications between and within scaffolds. Isolates at the front of the pathogens' expanding range tend to share lineage-specific structural variants, as confirmed by short-read sequencing. We identified, for the first time, 3 new mating type A locus alleles (5 in total) and 1 new potential mating type B locus allele (3 in total). Currently, only 2 mating type combinations, A1B1 and A2B2, are known to exist outside of Colombia. A systematic survey of the M. roreri transcriptome across 2 isolates identified an expanded candidate effector pool and provided evidence that effector candidate genes unique to the Moniliophthoras are preferentially expressed during the biotrophic phase of disease. Notably, M. roreri isolates in Costa Rica carry a chromosome segment duplication that has doubled the associated gene complement and includes secreted proteins and candidate effectors. Clonal reproduction of the haploid M. roreri genome has allowed lineages with unique genome structures and compositions to dominate as it expands its range, displaying a significant founder effect.

BASIDIN as a New Protein Effector of the Phytopathogen Causing Witche's Broom Disease in Cocoa

The fungus Moniliophthora perniciosa secretes protein effectors that manipulate the physiology of the host plant, but few effectors of this fungus have had their functions confirmed. We performed functional characterization of a promising candidate effector of M. perniciosa. The inoculation of rBASIDIN at 4 µmol L^-1 in the mesophyll of leaflets of Solanum lycopersicum caused symptoms of shriveling within 6 h without the presence of necrosis. However, when sprayed on the plant at a concentration of 11 µmol L^-1, it caused wilting symptoms only 2 h after application, followed by necrosis and cell death at 48 h. rBASIDIN applied to Theobroma cacao leaves at the same concentration caused milder symptoms. rBASIDIN caused hydrogen peroxide production in leaf tissue, damaging the leaf membrane and negatively affecting the photosynthetic rate of Solanum lycopersicum plants. Phylogenetic analysis indicated that BASIDIN has orthologs in other phytopathogenic basidiomycetes. Analysis of the transcripts revealed that BASIDIN and its orthologs are expressed in different fungal species, suggesting that this protein is differentially regulated in these basidiomycetes. Therefore, the results of applying BASIDIN allow the inference that it is an effector of the fungus M. perniciosa, with a strong potential to interfere in the defense system of the host plant.

Genomic and Pathogenicity Mechanisms of the Main Theobroma cacao L. Eukaryotic Pathogens: A Systematic Review

A set of diseases caused by fungi and oomycetes are responsible for large losses in annual world cocoa production. Managing the impact caused by these diseases is very complex because a common solution has yet to be found for different pathogens. In this context, the systematic knowledge of Theobroma cacao L. pathogens' molecular characteristics may help researchers understand the possibilities and limitations of cocoa disease management strategies. This work systematically organized and summarized the main findings of omics studies of T. cacao eukaryotic pathogens, focusing on the plant-pathogen interaction and production dynamics. Using the PRISMA protocol and a semiautomated process, we selected papers from the Scopus and Web of Science databases and collected data from the selected papers. From the initial 3169 studies, 149 were selected. The first author's affiliations were mostly from two countries, Brazil (55%) and the USA (22%). The most frequent genera were Moniliophthora (105 studies), Phytophthora (59 studies) and Ceratocystis (13 studies). The systematic review database includes papers reporting the whole-genome sequence from six cocoa pathogens and evidence of some necrosis-inducing-like proteins, which are common in T. cacao pathogen genomes. This review contributes to the knowledge about T. cacao diseases, providing an integrated discussion of T. cacao pathogens' molecular characteristics, common mechanisms of pathogenicity and how this knowledge is produced worldwide.

State of the Art of the Molecular Biology of the Interaction between Cocoa and Witches’ Broom Disease: A Systematic Review

Significant scientific advances to elucidate the Moniliophthora perniciosa pathosystem have been achieved in recent years, but the molecular biology of this pathogen-host interaction is still a field with many unanswered questions. In order to present insights at the molecular level, we present the first systematic review on the theme. All told, 1118 studies were extracted from public databases. Of these, 109 were eligible for the review, based on the inclusion and exclusion criteria. The results indicated that understanding the transition from the biotrophic-necrotrophic phase of the fungus is crucial for control of the disease. Proteins with strong biotechnological potential or that can be targets for pathosystem intervention were identified, but studies regarding possible applications are still limited. The studies identified revealed important genes in the M. perniciosa-host interaction and efficient molecular markers in the search for genetic variability and sources of resistance, with Theobroma cacao being the most common host. An arsenal of effectors already identified and not explored in the pathosystem were highlighted. This systematic review contributes to the understanding of the pathosystem at the molecular level, offering new insights and proposing different paths for the development of new strategies to control witches’ broom disease.

Chromosomal polymorphism of the Ceratocystis fimbriata species complex in Brazil

Ceratocystis fimbriata is an important pathogen that causes wilt in several plant species. Despite the importance of this pathogen, knowledge about its karyotypic polymorphism and genomic architecture is limited. The main objective of this study was to investigate the karyotype of isolates of the C. fimbriata species complex from different host plants and geographical origins in Brazil. First, the identity of the isolates was confirmed conducting multilocus sequence analysis (MLSA) phylogeny using β-tubulin (TUBB), translation elongation factor 1α (TEF-1α) and mating-type (MAT1 and MAT2) gene sequences. To investigate the chromosomal polymorphism, two conditions of pulsed-field gel electrophoresis (PFGE) were used and the karyotypes of the isolates obtained. The retrotransposon-microsatellite amplified polymorphism (REMAP) molecular marker was utilized to assess the genetic variability among isolates. In the MLSA utilizing the concatenated gene sequences, Ceratocystis cacaofunesta and C. fimbriata formed separate clades, but considerable variation among C. fimbriata isolates was observed. Polymorphism in chromosome number and size was found, indicating the existence of genomic differences among isolates and occurrence of chromosomal rearrangements in the species complex. The number of chromosomes varied from seven to nine and the estimated minimum chromosome sizes were estimated to be between 2.7 to 6.0 Mbp. Small polymorphic chromosomes ranging from 1.2 to 1.8 Mbp were observed in all isolates, raising the hypothesis that they could be supernumerary chromosomes. REMAP analysis revealed a high genetic variability and that isolates from the same host tend to group together in a same cluster. Our results bring new insights into the chromosomal diversity and genome organization of the C. fimbriata complex.

Moniliophthora perniciosa, the mushroom causing witches' broom disease of cacao: Insights into its taxonomy, ecology and host range in Brazil

Witches' broom caused by Moniliophthora perniciosa is the main disease of cacao (Theobroma cacao) in Brazil. The fungus is known to occur on other host families and these populations have been addressed in the literature as biotypes: C (Malvaceae); H (Malpighiaceae); L (Bignoniaceae) and S (Solanaceae). No complete elucidation of the phylogenetic relationships of isolates obtained from this disparate host range appears in the literature. One member of H (ex Heteropterys acutifolia) has been described as a distinct species. But should other biotypes be also recognized as distinct taxa? In the present study, a survey yielding 24 isolates of M. perniciosa from ten hosts and covering a wide range of geographic regions in Brazil was undertaken. These isolates were compared with those from T. cacao using three DNA regions for the phylogenetic analyses: ITS, LSU and RPB1. Morphology was also examined. All isolates in this study were found to belong to M. perniciosa, including the population from H. acutifolia, formerly treated as Moniliophthora brasiliensis but reduced here to a synonym of M. perniciosa. This species ranged from pathogenic to a previously unreported occurrence as a non-pathogenic endophyte in the Atlantic rainforest tree Allophylus edulis (Sapindaceae). M. perniciosa was recorded on a range of solanaceous hosts (16 species) over a wide variety of ecosystems. The ecological and evolutionary significance of these novel findings are discussed.

Genome sequence and effectorome of Moniliophthora perniciosa and Moniliophthora roreri subpopulations

Background

The hemibiotrophic pathogens Moniliophthora perniciosa (witches’ broom disease) and Moniliophthora roreri (frosty pod rot disease) are among the most important pathogens of cacao. Moniliophthora perniciosa has a broad host range and infects a variety of meristematic tissues in cacao plants, whereas M. roreri infects only pods of Theobroma and Herrania genera. Comparative pathogenomics of these fungi is essential to understand Moniliophthora infection strategies, therefore the detection and in silico functional characterization of effector candidates are important steps to gain insight on their pathogenicity.

Results

Candidate secreted effector proteins repertoire were predicted using the genomes of five representative isolates of M. perniciosa subpopulations (three from cacao and two from solanaceous hosts), and one representative isolate of M. roreri from Peru. Many putative effectors candidates were identified in M. perniciosa: 157 and 134 in cacao isolates from Bahia, Brazil; 109 in cacao isolate from Ecuador, 92 and 80 in wild solanaceous isolates from Minas Gerais (Lobeira) and Bahia (Caiçara), Brazil; respectively. Moniliophthora roreri showed the highest number of effector candidates, a total of 243. A set of eight core effectors were shared among all Moniliophthora isolates, while others were shared either between the wild solanaceous isolates or among cacao isolates. Mostly, candidate effectors of M. perniciosa were shared among the isolates, whereas in M. roreri nearly 50% were exclusive to the specie. In addition, a large number of cell wall-degrading enzymes characteristic of hemibiotrophic fungi were found. From these, we highlighted the proteins involved in cell wall modification, an enzymatic arsenal that allows the plant pathogens to inhabit environments with oxidative stress, which promotes degradation of plant compounds and facilitates infection.

Conclusions

The present work reports six genomes and provides a database of the putative effectorome of Moniliophthora, a first step towards the understanding of the functional basis of fungal pathogenicity.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4875-7) contains supplementary material, which is available to authorized users.

Saprotrophic proteomes of biotypes of the witches' broom pathogen Moniliophthora perniciosa

Nine geographically diverse Moniliophthora perniciosa (witches' broom disease pathogen) isolates were cultured in vitro. They included six C-biotypes differing in virulence on cacao (Theobroma cacao), two S-biotypes (solanaceous hosts), and an L-biotype (liana hosts). Mycelial growth rates and morphologies differed considerably, but no characters were observed to correlate with virulence or biotype. In plant inoculations using basidiospores, one C-biotype caused symptoms on tomato (an S-biotype host), adding to evidence of limited host adaptation in these biotypes. Mycelial proteomes were analysed by two-dimensional gel electrophoresis (2-DE), and 619 gel spots were indexed on all replicate gels of at least one strain. Multivariate analysis of gel spots discriminated the L-biotype, but not the S-biotypes, from the remaining strains. The proteomic similarity of the S- and C-biotypes is consistent with their reported lack of phylogenetic distinction. Sequences from tandem mass spectrometry of tryptic peptides from major 2-DE spots were matched with Moniliophthora genome and transcript sequences on NCBI and WBD Transcriptome Atlas databases. Protein-spot identifications indicated that M. perniciosa saprotrophic mycelial proteomes expressed functions potentially connected with a 'virulence life-style', including peroxiredoxin, heat-shock proteins, nitrilase, formate dehydrogenase, a prominent complement of aldo-keto reductases, mannitol-1-phosphate dehydrogenase, and central metabolism enzymes with proposed pathogenesis functions.

Development of novel microsatellites from Moniliophthora perniciosa, causal agent of the witches' broom disease of Theobroma cacao

Moniliophthora perniciosa is the causal agent of the witches' broom disease of cacao. Based on available genomic sequences, we identified 30 new microsatellite loci, which were analysed using 50 isolates from four populations sampled over a wide geographical area in Brazil, including three populations from the Amazon, the fungal putative centre of diversity, plus one from Bahia. Nine loci were polymorphic, with an average of 2.9 alleles per locus. The level of polymorphism observed was low, but these markers may allow the evaluation of pathogen diversity and the establishment of molecular standards for isolate fingerprinting to support cacao breeding.

Identification and characterization of a class III chitin synthase gene of Moniliophthora perniciosa, the fungus that causes witches' broom disease of cacao

Chitin synthase (CHS) is a glucosyltransferase that converts UDP-N-acetylglucosamine into chitin, one of the main components of fungal cell wall. Class III chitin synthases act directly in the formation of the cell wall. They catalyze the conversion of the immediate precursor of chitin and are responsible for the majority of chitin synthesis in fungi. As such, they are highly specific molecular targets for drugs that can inhibit the growth and development of fungal pathogens. In this work, we have identified and characterized a chitin synthase gene of Moniliophthora perniciosa (Mopchs) by primer walking. The complete gene sequence is 3,443 bp, interrupted by 13 small introns, and comprises a cDNA with an ORF with 2,739 bp, whose terminal region was experimentally determined, encoding a protein with 913 aa that harbors all the motifs and domains typically found in class III chitin synthases. This is the first report on the characterization of a chitin synthase gene, its mature transcription product, and its putative protein in basidioma and secondary mycelium stages of M. perniciosa, a basidiomycotan fungus that causes witches' broom disease of cacao.

A genome survey of Moniliophthora perniciosa gives new insights into Witches' Broom Disease of cacao

Background

The basidiomycete fungus Moniliophthora perniciosa is the causal agent of Witches' Broom Disease (WBD) in cacao (Theobroma cacao). It is a hemibiotrophic pathogen that colonizes the apoplast of cacao's meristematic tissues as a biotrophic pathogen, switching to a saprotrophic lifestyle during later stages of infection. M. perniciosa, together with the related species M. roreri, are pathogens of aerial parts of the plant, an uncommon characteristic in the order Agaricales. A genome survey (1.9× coverage) of M. perniciosa was analyzed to evaluate the overall gene content of this phytopathogen.

Results

Genes encoding proteins involved in retrotransposition, reactive oxygen species (ROS) resistance, drug efflux transport and cell wall degradation were identified. The great number of genes encoding cytochrome P450 monooxygenases (1.15% of gene models) indicates that M. perniciosa has a great potential for detoxification, production of toxins and hormones; which may confer a high adaptive ability to the fungus. We have also discovered new genes encoding putative secreted polypeptides rich in cysteine, as well as genes related to methylotrophy and plant hormone biosynthesis (gibberellin and auxin). Analysis of gene families indicated that M. perniciosa have similar amounts of carboxylesterases and repertoires of plant cell wall degrading enzymes as other hemibiotrophic fungi. In addition, an approach for normalization of gene family data using incomplete genome data was developed and applied in M. perniciosa genome survey.

Conclusion

This genome survey gives an overview of the M. perniciosa genome, and reveals that a significant portion is involved in stress adaptation and plant necrosis, two necessary characteristics for a hemibiotrophic fungus to fulfill its infection cycle. Our analysis provides new evidence revealing potential adaptive traits that may play major roles in the mechanisms of pathogenicity in the M. perniciosa/cacao pathosystem.

Moniliophthora perniciosa, the causal agent of witches' broom disease of cacao: what's new from this old foe?

Moniliophthora perniciosa (=Crinipellis perniciosa) causes one of the three main fungal diseases of Theobroma cacao (cacao), the source of chocolate. This pathogen causes Witches' broom disease (WBD) and has brought about severe economic losses in all of the cacao-growing regions to which it has spread with yield reductions that range from 50 to 90%. Cacao production in South America reflects the severity of this pathogen, as the yields in most of the infected regions have not returned to pre-outbreak levels, even with the introduction of resistant varieties. In this review we give a brief historical account and summarize the current state of knowledge focusing on developments in the areas of systematics, fungal physiology, biochemistry, genomics and gene expression in an attempt to highlight this disease. Moniliophthora perniciosa is a hemibiotrophic fungus with two distinct growth phases. The ability to culture a biotrophic-like phase in vitro along with new findings derived from the nearly complete genome and expression studies clearly show that these different fungal growth phases function under distinct metabolic parameters. These new findings have greatly improved our understanding of this fungal/host interaction and we may be at the crossroads of understanding how hemibiotrophic fungal plant pathogens cause disease in other crops.

HISTORICAL SUMMARY OF WBD

The first WDB symptoms appear to have been described in the diaries of Alexandre Rodrigues Ferreira (described as lagartão; meaning big lizard) from his observations of cacao trees in 1785 and 1787 in Amazonia, which is consistent with the generally accepted idea that M. perniciosa, like its main host T. cacao, evolved in this region. The disease subsequently arrived in Surinam in 1895. WBD moved rapidly, spreading to Guyana in 1906, Ecuador in 1918, Trinidad in 1928, Colombia in 1929 and Grenada in 1948. In each case, cacao production was catastrophically affected with yield reductions of 50-90%. After the arrival of M. perniciosa in Bahia in 1989, Brazil went from being the world's 3rd largest producer of cacao (347 000 tonnes in 1988-1990; c. 15% of the total world production at that time) to a net importer (141 000 tonnes in 1998-2000). Fortunately for chocolate lovers, other regions of the world such as West Africa and South East Asia have not yet been affected by this disease and have expanded production to meet growing world demand (predicted to reach 3 700 000 tonnes by 2010).

CLASSIFICATION

Moniliophthora perniciosa (Stahel) Aime & Phillips-Mora: super-kingdom Eukaryota; kingdom Fungi; phylum Basidiomycota; subphylum Agaricomycotina; class Agaricomycetes; subclass Agaricomycetidae; order Agaricales; family Marasmiaceae; genus Moniliophthora.

USEFUL WEBSITES

http://www.lge.ibi.unicamp.br/vassoura/, http://nt.ars-grin.gov/taxadescriptions/keys/TrichodermaIndex.cfm, http://www.worldcocoafoundation.org/info-center/research-updates.asp, http://www.ars.usda.gov/ba/psi/spcl.

Differential gene expression between the biotrophic-like and saprotrophic mycelia of the witches' broom pathogen Moniliophthora perniciosa

Moniliophthora perniciosa is a hemibiotrophic fungus that causes witches' broom disease (WBD) in cacao. Marked dimorphism characterizes this fungus, showing a monokaryotic or biotrophic phase that causes disease symptoms and a later dikaryotic or saprotrophic phase. A combined strategy of DNA microarray, expressed sequence tag, and real-time reverse-transcriptase polymerase chain reaction analyses was employed to analyze differences between these two fungal stages in vitro. In all, 1,131 putative genes were hybridized with cDNA from different phases, resulting in 189 differentially expressed genes, and 4,595 reads were clusterized, producing 1,534 unigenes. The analysis of these genes, which represent approximately 21% of the total genes, indicates that the biotrophic-like phase undergoes carbon and nitrogen catabolite repression that correlates to the expression of phytopathogenicity genes. Moreover, downregulation of mitochondrial oxidative phosphorylation and the presence of a putative ngr1 of Saccharomyces cerevisiae could help explain its lower growth rate. In contrast, the saprotrophic mycelium expresses genes related to the metabolism of hexoses, ammonia, and oxidative phosphorylation, which could explain its faster growth. Antifungal toxins were upregulated and could prevent the colonization by competing fungi. This work significantly contributes to our understanding of the molecular mechanisms of WBD and, to our knowledge, is the first to analyze differential gene expression of the different phases of a hemibiotrophic fungus.

Comparative analysis of expressed genes from cacao meristems infected by Moniliophthora perniciosa

BACKGROUND AND AIMS

Witches' broom disease is caused by the hemibiotrophic basidiomycete Moniliophthora perniciosa, and is one of the most important diseases of cacao in the western hemisphere. Because very little is known about the global process of such disease development, expressed sequence tags (ESTs) were used to identify genes expressed during the Theobroma cacao-Moniliophthora perniciosa interaction.

METHODS

Two cDNA libraries corresponding to the resistant (RT) and susceptible (SP) cacao-M. perniciosa interactions were constructed from total RNA, using the DB SMART Creator cDNA library kit (Clontech). Clones were randomly selected, sequenced from the 5' end and analysed using bioinformatics tools including in silico analysis of the differential gene expression.

KEY RESULTS

A total of 6884 ESTs were generated from the RT and SP cDNA libraries. These ESTs were composed of 2585 singlets and 341 contigs for a total of 2926 non-redundant sequences. The redundancy of the libraries was low and their specificity high when compared with the few other cacao libraries already published. Sequence analysis allowed the assignment of a putative functional category for 54 % of sequences, whereas approx. 22 % of sequences corresponded to unknown function and approx. 24 % of sequences did not show any significant similarity with other proteins present in the database. Despite the similar overall distribution of the sequences in functional categories between the two libraries, qualitative differences were observed. Genes involved during the defence response to pathogen infection or in programmed cell death were identified, such as pathogenesis related-proteins, trypsin inhibitor or oxalate oxidase, and some of them showed an in silico differential expression between the resistant and the susceptible interactions.

CONCLUSIONS

As far as is known this is the first EST resource from the cacao-M. perniciosa interaction and it is believed that it will provide a significant contribution to the understanding of the molecular mechanisms of the resistance and susceptibility of cacao to M. perniciosa, to develop strategies to control witches' broom, and as a source of polymorphism for molecular marker development and marker-assisted selection.

Characterization of necrosis and ethylene-inducing proteins (NEP) in the basidiomycete Moniliophthora perniciosa, the causal agent of witches' broom in Theobroma cacao

The hemibiotrophic basidiomycete Moniliophthora perniciosa causes witches' broom disease of Theobroma cacao. Analysis of the M. perniciosa draft genome led to the identification of three putative genes encoding necrosis and ethylene-inducing proteins (MpNEPs), which are apparently located on the same chromosome. MpNEP1 and 2 have highly similar sequences and are able to induce necrosis and ethylene emission in tobacco and cacao leaves. MpNEP1 is expressed in both biotrophic and saprotrophic mycelia, the protein behaves as an oligomer in solution and is very sensitive to temperature. MpNEP2 is expressed mainly in biotrophic mycelia, is present as a monomer in solution at low concentrations (<40 microM) and is able to recover necrosis activity after boiling. These differences indicate that similar NEPs can have distinct physical characteristics and suggest possible complementary roles during the disease development for both proteins. This is the first report of NEP1-like proteins in a basidiomycete.