Co-expression of two genes, a chitinase (chit42) and proteinase (prb1), implicated in mycoparasitism byTrichoderma hamatum

Functions of reactive oxygen species in apoptosis and ganoderic acid biosynthesis in Ganoderma lucidum

Ganoderma lucidum is a medicinal fungus that is widely used in traditional medicine. Fungal PacC is recognized as an important transcription factor that functions during adaptation to environmental pH, fungal development and secondary metabolism. Previous studies have revealed that GlPacC plays important roles in mycelial growth, fruiting body development and ganoderic acid (GA) biosynthesis. In this study, using a terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay, we found that the apoptosis level was increased when PacC was silenced. The transcript and activity levels of caspase-like proteins were significantly increased in the PacC-silenced (PacCi) strains compared with the control strains. Silencing PacC also resulted in an increased reactive oxygen species (ROS) levels (∼2-fold) and decreased activity levels of enzymes involved in the antioxidant system. Further, we found that the intracellular ROS levels contributed to apoptosis and GA biosynthesis. Adding N-acetyl-cysteine and vitamin C decreased intracellular ROS and resulted in the inhibition of apoptosis in the PacCi strains. Additionally, the GA biosynthesis was different between the control strains and the PacCi strains after intracellular ROS was eliminated. Taken together, the findings showed that silencing PacC can result in an intracellular ROS burst, which increases cell apoptosis and GA biosynthesis levels. Our study provides novel insight into the functions of PacC in filamentous fungi.

Molecular heterozygosity and genetic exploitations of Trichoderma inter-fusants enhancing tolerance to fungicides and mycoparasitism against Sclerotium rolfsii Sacc

Protoplast fusion is an imperative tool to develop Trichoderma inter-fusants having desire traits through genetic manipulation. Study designed to develop diverse Trichoderma fusants for fungicide tolerance (Mancozeb, Thiram, Tebuconazole, and Carbendazim) and enhanced mycoparasitic activity against Sclerotium rolfsii sacc. The mycoparasitic T. virens NBAII Tvs12 and fungicide tolerant T. koningii MTCC 796 were utilized for protoplast fusion. The derived inter-fusants were subjected to diploidization using d-camphor in minimal media followed by successive three sub culturing onto potato dextrose agar to obtain 36 stable fusants. The stable fusants were employed for conidial size, fungicide tolerance, mycoparasitism, gene specific SSR amplification and molecular heterozygosity analysis. The results explained that 22 homozygous mutants illustrated characteristic of either one parental strain and 14 heterozygous recombinants depicted traits of both parental strains. The antagonistic activity of fusants against S. rolfsii depicted highest growth inhibition (87.91%) by potent inter-fusant (Fu 21) with improved fungicide tolerance capacity. The molecular study revealed highest observed heterozygocity (0.544), coefficient of gene differentiation (0.526) and gene flow (0.387) by Fu 21 indicating better genetic exploitation of parental strains into that fusant with good genetic purity. Principal coordinate analysis of fusants and parental strains exhibited 65.07% total variation and confirmed the scattering pattern matched with UPGMA clustering pattern. The stable heterozygous Fu 21 derived from inter-fusion between Tvs 12 and MTCC 796 might be useful to practice eco-friendly bioformulation tolerance to fungicides for effective integrated stem rot disease management in groundnut.

Temporal analysis of the magnaporthe oryzae proteome during conidial germination and cyclic AMP (cAMP)-mediated appressorium formation

Rice blast disease caused by Magnaporthe oryzae is one of the most serious threats to global rice production. During the earliest stages of rice infection, M. oryzae conidia germinate on the leaf surface and form a specialized infection structure termed the appressorium. The development of the appressorium represents the first critical stage of infectious development. A total of 3200 unique proteins were identified by nanoLC-MS/MS in a temporal study of conidial germination and cAMP-induced appressorium formation in M. oryzae. Using spectral counting based label free quantification, observed changes in relative protein abundance during the developmental process revealed changes in the cell wall biosynthetic machinery, transport functions, and production of extracellular proteins in developing appressoria. One hundred and sixty-six up-regulated and 208 down-regulated proteins were identified in response to cAMP treatment. Proteomic analysis of a cAMP-dependent protein kinase A mutant that is compromised in the ability to form appressoria identified proteins whose developmental regulation is dependent on cAMP signaling. Selected reaction monitoring was used for absolute quantification of four regulated proteins to validate the global proteomics data and confirmed the germination or appressorium specific regulation of these proteins. Finally, a comparison of the proteome and transcriptome was performed and revealed little correlation between transcript and protein regulation. A subset of regulated proteins were identified whose transcripts show similar regulation patterns and include many of the most strongly regulated proteins indicating a central role in appressorium formation. A temporal quantitative RT-PCR analysis confirmed a strong correlation between transcript and protein abundance for some but not all genes. Collectively, the data presented here provide the first comprehensive view of the M. oryzae proteome during early infection-related development and highlight biological processes important for pathogenicity.

Cloning and characterization ofbgn16·3, coding for a β-1,6-glucanase expressed duringTrichoderma harzianummycoparasitism

AIMS

To clone and characterize the gene coding for BGN16.3, a beta-1,6-glucanase putatively implicated in mycoparasitism by Trichoderma harzianum, a biocontrol agent used against plant pathogenic fungi.

METHODS AND RESULTS

Using degenerate primed PCR and cDNA library screening, we have cloned the cDNA coding BGN16.3. bgn16.3 showed a significant sequence identity (50%) to bgn16.1; however, they both have low identity to the previously cloned bgn16.2, allowing the identification of amino acid sequences putatively involved in the common catalytic activity of the three proteins. bgn16.3 is a single-copy gene and highly homologous sequences are present in all tested Trichoderma species. bgn16.3 expression pattern is analysed by Northern blot, finding that it is expressed during the interaction of T. harzianum CECT 2413 with Botrytis cinerea, supporting the implication of the enzyme in the mycoparasitic process.

CONCLUSIONS

The cloned bgn16.3 completes the knowledge on the beta-1,6-glucanase isozyme system from T. harzianum CECT 2413. A highly homologous gene is present in all analysed Trichoderma strains. bgn16.3 is expressed under few specific conditions, including the mycoparasitic process.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study contributes to the knowledge of beta-1,6-glucanases. It implicates this group of enzymes in the mycoparasitism by some biocontrol agents such as T. harzianum.

Characterization of genes encoding novel peptidases in the biocontrol fungus Trichoderma harzianum CECT 2413 using the TrichoEST functional genomics approach

Proteolytic enzymes (EC 3.4) secreted by Trichoderma strains are receiving increasing attention because of their potential implication in the Trichoderma biocontrol abilities. We have used an expressed sequence tag (EST) approach to identify genes encoding extracellular peptidases in T. harzianum CECT 2413 grown under several biocontrol-related conditions. Based on BlastX results and Gene Ontology annotation, a total of 61 (among 3478) unique sequences (unisequences) were predicted to encode enzymes with peptidase activity, three corresponding to secreted peptidases already known from this Trichoderma strain (PAPA, PRA1 and P6281). Further manual screening based on the functional identity and cellular location of the best matches revealed ten unisequences encoding novel extracellular peptidases. We report the characterization of the corresponding genes as well as a potential orthologous gene of the intracellular peptidase PAPB from T. asperellum. In each case, full-length coding sequences were obtained, and deduced proteins were compared at phylogenetic level with peptidases from other organisms. T. harzianum CECT 2413 novel peptidases included six serine endopeptidases (EC 3.4.21) belonging to the families S1, S8 and S53, three aspartic endopeptidases (EC 3.4.23) of the family A1, one metallo-endopeptidase (EC 3.4.24) of the family M35, and one aminopeptidase (EC 3.4.11) of the family M28. Results obtained by Northern blot analyses demonstrated that the genes within a family are differentially regulated in response to different culture conditions, suggesting that they have diverse functional roles.

Fungal and plant gene expression during the colonization of cacao seedlings by endophytic isolates of four Trichoderma species

Endophytic isolates of Trichoderma species are being considered as biocontrol agents for diseases of Theobroma cacao (cacao). Gene expression was studied during the interaction between cacao seedlings and four endophytic Trichoderma isolates, T. ovalisporum-DIS 70a, T. hamatum-DIS 219b, T. harzianum-DIS 219f, and Trichoderma sp.-DIS 172ai. Isolates DIS 70a, DIS 219b, and DIS 219f were mycoparasitic on the pathogen Moniliophthora roreri, and DIS 172ai produced metabolites that inhibited growth of M. roreri in culture. ESTs (116) responsive to endophytic colonization of cacao were identified using differential display and their expression analyzed using macroarrays. Nineteen cacao ESTs and 17 Trichoderma ESTs were chosen for real-time quantitative PCR analysis. Seven cacao ESTs were induced during colonization by the Trichoderma isolates. These included putative genes for ornithine decarboxylase (P1), GST-like proteins (P4), zinc finger protein (P13), wound-induced protein (P26), EF-calcium-binding protein (P29), carbohydrate oxidase (P59), and an unknown protein (U4). Two plant ESTs, extensin-like protein (P12) and major intrinsic protein (P31), were repressed due to colonization. The plant gene expression profile was dependent on the Trichoderma isolate colonizing the cacao seedling. The fungal ESTs induced in colonized cacao seedlings also varied with the Trichoderma isolate used. The most highly induced fungal ESTs were putative glucosyl hydrolase family 2 (F3), glucosyl hydrolase family 7 (F7), serine protease (F11), and alcohol oxidase (F19). The pattern of altered gene expression suggests a complex system of genetic cross talk occurs between the cacao tree and Trichoderma isolates during the establishment of the endophytic association.

Identification of novel Trichoderma hamatum genes expressed during mycoparasitism using subtractive hybridisation

Subtractive hybridisation was used to target novel genes involved in the mycoparasitic interaction of the biocontrol agent Trichoderma hamatum with the phytopathogen Sclerotinia sclerotiorum. Nineteen novel T. hamatum genes were identified that showed increased expression during mycoparasitism compared to a T. hamatum control. Sequence analysis revealed some cDNA fragments had similarity to known fungal or bacterial genes whereas others had no similarity to any genes previously described. Only one of the novel genes has been characterised in another Trichoderma species, the Trichoderma reesei hex1gene. The proteins encoded by the novel genes included three monooxygenases, a metalloendopeptidase, a gluconate dehydrogenase, an endonuclease and a proton ATPase.