Hybrid de novo genome-reassembly reveals new insights on pathways and pathogenicity determinants in rice blast pathogen Magnaporthe oryzae RMg_Dl

Antifungal plant flavonoids identified in silico with potential to control rice blast disease caused by Magnaporthe oryzae

Rice blast disease, caused by the fungus Magnaporthe oryzae, poses a severe threat to rice production, particularly in Asia where rice is a staple food. Concerns over fungicide resistance and environmental impact have sparked interest in exploring natural fungicides as potential alternatives. This study aimed to identify highly potent natural fungicides against M. oryzae to combat rice blast disease, using advanced molecular dynamics techniques. Four key proteins (CATALASE PEROXIDASES 2, HYBRID PKS-NRPS SYNTHETASE TAS1, MANGANESE LIPOXYGENASE, and PRE-MRNA-SPLICING FACTOR CEF1) involved in M. oryzae's infection process were identified. A list of 30 plant metabolites with documented antifungal properties was compiled for evaluation as potential fungicides. Molecular docking studies revealed that 2-Coumaroylquinic acid, Myricetin, Rosmarinic Acid, and Quercetin exhibited superior binding affinities compared to reference fungicides (Azoxystrobin and Tricyclazole). High throughput molecular dynamics simulations were performed, analyzing parameters like RMSD, RMSF, Rg, SASA, hydrogen bonds, contact analysis, Gibbs free energy, and cluster analysis. The results revealed stable interactions between the selected metabolites and the target proteins, involving important hydrogen bonds and contacts. The SwissADME server analysis indicated that the metabolites possess fungicide properties, making them effective and safe fungicides with low toxicity to the environment and living beings. Additionally, bioactivity assays confirmed their biological activity as nuclear receptor ligands and enzyme inhibitors. Overall, this study offers valuable insights into potential natural fungicides for combating rice blast disease, with 2-Coumaroylquinic acid, Myricetin, Rosmarinic Acid, and Quercetin standing out as promising and environmentally friendly alternatives to conventional fungicides. These findings have significant implications for developing crop protection strategies and enhancing global food security, particularly in rice-dependent regions.

Deciphering the Genomic Landscape and Virulence Mechanisms of the Wheat Powdery Mildew Pathogen Blumeria graminis f. sp. tritici Wtn1: Insights from Integrated Genome Assembly and Conidial Transcriptomics

A high-quality genome sequence from an Indian isolate of Blumeria graminis f. sp. tritici Wtn1, a persistent threat in wheat farming, was obtained using a hybrid method. The assembly of over 9.24 million DNA-sequence reads resulted in 93 contigs, totaling a 140.61 Mb genome size, potentially encoding 8480 genes. Notably, more than 73.80% of the genome, spanning approximately 102.14 Mb, comprises retro-elements, LTR elements, and P elements, influencing evolution and adaptation significantly. The phylogenomic analysis placed B. graminis f. sp. tritici Wtn1 in a distinct monocot-infecting clade. A total of 583 tRNA anticodon sequences were identified from the whole genome of the native virulent strain B. graminis f. sp. tritici, which comprises distinct genome features with high counts of tRNA anticodons for leucine (70), cysteine (61), alanine (58), and arginine (45), with only two stop codons (Opal and Ochre) present and the absence of the Amber stop codon. Comparative InterProScan analysis unveiled "shared and unique" proteins in B. graminis f. sp. tritici Wtn1. Identified were 7707 protein-encoding genes, annotated to different categories such as 805 effectors, 156 CAZymes, 6102 orthologous proteins, and 3180 distinct protein families (PFAMs). Among the effectors, genes like Avra10, Avrk1, Bcg-7, BEC1005, CSEP0105, CSEP0162, BEC1016, BEC1040, and HopI1 closely linked to pathogenesis and virulence were recognized. Transcriptome analysis highlighted abundant proteins associated with RNA processing and modification, post-translational modification, protein turnover, chaperones, and signal transduction. Examining the Environmental Information Processing Pathways in B. graminis f. sp. tritici Wtn1 revealed 393 genes across 33 signal transduction pathways. The key pathways included yeast MAPK signaling (53 genes), mTOR signaling (38 genes), PI3K-Akt signaling (23 genes), and AMPK signaling (21 genes). Additionally, pathways like FoxO, Phosphatidylinositol, the two-component system, and Ras signaling showed significant gene representation, each with 15-16 genes, key SNPs, and Indels in specific chromosomes highlighting their relevance to environmental responses and pathotype evolution. The SNP and InDel analysis resulted in about 3.56 million variants, including 3.45 million SNPs, 5050 insertions, and 5651 deletions within the whole genome of B. graminis f. sp. tritici Wtn1. These comprehensive genome and transcriptome datasets serve as crucial resources for understanding the pathogenicity, virulence effectors, retro-elements, and evolutionary origins of B. graminis f. sp. tritici Wtn1, aiding in developing robust strategies for the effective management of wheat powdery mildew.

RNAPII Degradation Factor Def1 Is Required for Development, Stress Response, and Full Virulence of Magnaporthe oryzae

The RNA polymerase II degradation factor Degradation Factor 1 (Def1) is important for DNA damage repair and plays various roles in eukaryotes; however, the biological role in plant pathogenic fungi is still unknown. In this study, we investigated the role of Def1 during the development and infection of the rice blast fungus Magnaporthe oryzae. The deletion mutant of Def1 displayed slower mycelial growth, less conidial production, and abnormal conidial morphology. The appressoria of Δdef1 was impaired in the penetration into host cells, mainly due to blocking in the utilization of conidial storages, such as glycogen and lipid droplets. The invasive growth of the Δdef1 mutant was also retarded and accompanied with the accumulation of reactive oxygen species (ROS) inside the host cells. Furthermore, compared with the wild type, Δdef1 was more sensitive to multiple stresses, such as oxidative stress, high osmotic pressure, and alkaline/acidic pH. Interestingly, we found that Def1 was modified by O-GlcNAcylation at Ser232, which was required for the stability of Def1 and its function in pathogenicity. Taken together, the O-GlcNAc modified Def1 is required for hyphae growth, conidiation, pathogenicity, and stress response in M. oryzae. This study reveals a novel regulatory mechanism of O-GlcNAc-mediated Def1 in plant pathogenic fungi.

Docsubty: FLALipid extract derived from newly isolated Rhodotorula toruloides LAB-07 for cosmetic applications

Rhodotorula toruloides is a non-conventional yeast with a natural carotenoid pathway. In particular, R. toruloides is an oleaginous yeast that can accumulate lipids in high content, thereby gaining interest as a promising industrial host. In this study, we isolated and taxonomically identified a new R. toruloides LAB-07 strain. De novo genome assembly using PacBio and Illumina hybrid platforms yielded 27 contigs with a 20.78 Mb genome size. Subsequent genome annotation analysis based on RNA-seq predicted 5296 protein-coding genes, including the fatty acid production pathway. We compared lipid production under different media; it was highest in the yeast extract salt medium with glycerol as a carbon source. Polyunsaturated α-linolenic acid was detected among the fatty acids, and docking phosphatidylcholine as a substrate to modeled Fad2, which annotated as Δ12-fatty acid desaturase showed bifunctional Δ12, 15-desaturation is structurally possible in that the distances between the diiron center and the carbon-carbon bond in which desaturation occurs were similar to those of structurally identified mouse stearoyl-CoA desaturase. Finally, the applicability of the extracted total lipid fraction of R. toruloides was investigated, demonstrating an increase in filaggrin expression and suppression of heat-induced MMP-1 expression when applied to keratinocytes, along with the additional antioxidant activity. This work presents a new R. toruloides LAB-07 strain with genomic and lipidomic data, which would help understand the physiology of R. toruloides. Also, the various skin-related effect of R. toruloides lipid extract indicates its potential usage as a promising cosmetic ingredient.

Structured Framework and Genome Analysis of Magnaporthe grisea Inciting Pearl Millet Blast Disease Reveals Versatile Metabolic Pathways, Protein Families, and Virulence Factors

Magnaporthe grisea (T.T. Herbert) M.E. Barr is a major fungal phytopathogen that causes blast disease in cereals, resulting in economic losses worldwide. An in-depth understanding of the basis of virulence and ecological adaptation of M. grisea is vital for devising effective disease management strategies. Here, we aimed to determine the genomic basis of the pathogenicity and underlying biochemical pathways in Magnaporthe using the genome sequence of a pearl millet-infecting M. grisea PMg_Dl generated by dual NGS techniques, Illumina NextSeq 500 and PacBio RS II. The short and long nucleotide reads could be draft assembled in 341 contigs and showed a genome size of 47.89 Mb with the N50 value of 765.4 Kb. Magnaporthe grisea PMg_Dl showed an average nucleotide identity (ANI) of 86% and 98% with M. oryzae and Pyricularia pennisetigena, respectively. The gene-calling method revealed a total of 10,218 genes and 10,184 protein-coding sequences in the genome of PMg_Dl. InterProScan of predicted protein showed a distinct 3637 protein families and 695 superfamilies in the PMg_Dl genome. In silico virulence analysis revealed the presence of 51VFs and 539 CAZymes in the genome. The genomic regions for the biosynthesis of cellulolytic endo-glucanase and beta-glucosidase, as well as pectinolytic endo-polygalacturonase, pectin-esterase, and pectate-lyases (pectinolytic) were detected. Signaling pathways modulated by MAPK, PI3K-Akt, AMPK, and mTOR were also deciphered. Multicopy sequences suggestive of transposable elements such as Type LTR, LTR/Copia, LTR/Gypsy, DNA/TcMar-Fot1, and Type LINE were recorded. The genomic resource presented here will be of use in the development of molecular marker and diagnosis, population genetics, disease management, and molecular taxonomy, and also provide a genomic reference for ascomycetous genome investigations in the future.

Understanding the Dynamics of Blast Resistance in Rice-Magnaporthe oryzae Interactions

Rice is a global food grain crop for more than one-third of the human population and a source for food and nutritional security. Rice production is subjected to various stresses; blast disease caused by Magnaporthe oryzae is one of the major biotic stresses that has the potential to destroy total crop under severe conditions. In the present review, we discuss the importance of rice and blast disease in the present and future global context, genomics and molecular biology of blast pathogen and rice, and the molecular interplay between rice–M. oryzae interaction governed by different gene interaction models. We also elaborated in detail on M. oryzae effector and Avr genes, and the role of noncoding RNAs in disease development. Further, rice blast resistance QTLs; resistance (R) genes; and alleles identified, cloned, and characterized are discussed. We also discuss the utilization of QTLs and R genes for blast resistance through conventional breeding and transgenic approaches. Finally, we review the demonstrated examples and potential applications of the latest genome-editing tools in understanding and managing blast disease in rice.

Deciphering core phyllomicrobiome assemblage on rice genotypes grown in contrasting agroclimatic zones: implications for phyllomicrobiome engineering against blast disease

BACKGROUND

With its adapted microbial diversity, the phyllosphere contributes microbial metagenome to the plant holobiont and modulates a host of ecological functions. Phyllosphere microbiome (hereafter termed phyllomicrobiome) structure and the consequent ecological functions are vulnerable to a host of biotic (Genotypes) and abiotic factors (Environment) which is further compounded by agronomic transactions. However, the ecological forces driving the phyllomicrobiome assemblage and functions are among the most understudied aspects of plant biology. Despite the reports on the occurrence of diverse prokaryotic phyla such as Proteobacteria, Firmicutes, Bacteroides, and Actinobacteria in phyllosphere habitat, the functional characterization leading to their utilization for agricultural sustainability is not yet explored. Currently, the metabarcoding by Next-Generation-Sequencing (mNGS) technique is a widely practised strategy for microbiome investigations. However, the validation of mNGS annotations by culturomics methods is not integrated with the microbiome exploration program. In the present study, we combined the mNGS with culturomics to decipher the core functional phyllomicrobiome of rice genotypes varying for blast disease resistance planted in two agroclimatic zones in India. There is a growing consensus among the various stakeholder of rice farming for an ecofriendly method of disease management. Here, we proposed phyllomicrobiome assisted rice blast management as a novel strategy for rice farming in the future.

RESULTS

The tropical "Island Zone" displayed marginally more bacterial diversity than that of the temperate 'Mountain Zone' on the phyllosphere. Principal coordinate analysis indicated converging phyllomicrobiome profiles on rice genotypes sharing the same agroclimatic zone. Interestingly, the rice genotype grown in the contrasting zones displayed divergent phyllomicrobiomes suggestive of the role of environment on phyllomicrobiome assembly. The predominance of phyla such as Proteobacteria, Actinobacteria, and Firmicutes was observed in the phyllosphere irrespective of the genotypes and climatic zones. The core-microbiome analysis revealed an association of Acidovorax, Arthrobacter, Bacillus, Clavibacter, Clostridium, Cronobacter, Curtobacterium, Deinococcus, Erwinia, Exiguobacterium, Hymenobacter, Kineococcus, Klebsiella, Methylobacterium, Methylocella, Microbacterium, Nocardioides, Pantoea, Pedobacter, Pseudomonas, Salmonella, Serratia, Sphingomonas and Streptomyces on phyllosphere. The linear discriminant analysis (LDA) effect size (LEfSe) method revealed distinct bacterial genera in blast-resistant and susceptible genotypes, as well as mountain and island climate zones. SparCC based network analysis of phyllomicrobiome showed complex intra-microbial cooperative or competitive interactions on the rice genotypes. The culturomic validation of mNGS data confirmed the occurrence of Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, and Sphingomonas in the phyllosphere. Strikingly, the contrasting agroclimatic zones showed genetically identical bacterial isolates suggestive of vertical microbiome transmission. The core-phyllobacterial communities showed secreted and volatile compound mediated antifungal activity on M. oryzae. Upon phyllobacterization (a term coined for spraying bacterial cells on the phyllosphere), Acinetobacter, Aureimonas, Pantoea, and Pseudomonas conferred immunocompetence against blast disease. Transcriptional analysis revealed activation of defense genes such as OsPR1.1, OsNPR1, OsPDF2.2, OsFMO, OsPAD4, OsCEBiP, and OsCERK1 in phyllobacterized rice seedlings.

CONCLUSIONS

PCoA indicated the key role of agro-climatic zones to drive phyllomicrobiome assembly on the rice genotypes. The mNGS and culturomic methods showed Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, and Sphingomonas as core phyllomicrobiome of rice. Genetically identical Pantoea intercepted on the phyllosphere from the well-separated agroclimatic zones is suggestive of vertical transmission of phyllomicrobiome. The phyllobacterization showed potential for blast disease suppression by direct antibiosis and defense elicitation. Identification of functional core-bacterial communities on the phyllosphere and their co-occurrence dynamics presents an opportunity to devise novel strategies for rice blast management through phyllomicrobiome reengineering in the future.

Antifungal and defense elicitor activity of Potassium phosphite against fungal blast disease on ptxD-OE transgenic indica rice and its acceptor parent

In rice farming, the blast disease caused by Magnaporthe oryzae (T.T. Hebert) M.E. Barr. is one of the primary production constraints worldwide. The current blast management options such as blast-resistant varieties and spraying fungicides are neither durable nor commercially and environmentally compatible. In the present study, we investigated the antifungal and defense elicitor activity of potassium phosphite (Phi) against M. oryzae on elite rice cultivar BPT5204 (popularly known as Samba Mahsuri in India) and its transgenic rice variant (ptxD-OE) over-expressing a phosphite dehydrogenase enzyme. The Phi was evaluated both preventively and curatively on rice genotypes where the preventive spray of Phi outperformed the Phi curative application with significant reductions in both rice blast severity (35.67-60.49%) and incidence (22.27-53.25%). Moreover, the application of Phi increased the levels of photosynthetic pigments (Chlorophyll and Carotenoids) coupled with increased activity of defense enzymes (PAL, SOD, and APx). Besides, Phi application also induced the expression of defense-associated genes (OsCEBiP and OsPDF2.2) in the rice leaf. Furthermore, the Phi application reduced the reactive Malondialdehyde (lipid peroxidation) to minimize the cellular damage incited by Magnaporthe in rice. Overall, the present study showed the potential of Phi for blast suppression on rice as an alternative to the current excessive use of toxic fungicides.