Search

Summary: Rice cultivars from japonica and indica lineage possess differential resistance against blast fungus as a result of genetic divergence. Whether different rice cultivars also show distinct metabolomic changes in response to P. oryzae, and their role in host resistance, are poorly understood. Here, we examine the responses of six different rice cultivars from japonica and indica lineage challenged with P. oryzae. Both susceptible and resistant rice cultivars expressed several metabolites exclusively during P. oryzae infection, including the saponin Bayogenin 3‐O‐cellobioside. Bayogenin 3‐O‐cellobioside level in infected rice directly correlated with their resistant attributes. These findings reveal, for the first time to our knowledge that besides oat, other grass plants including rice produces protective saponins. Our study provides insight into the role of pathogen‐mediated metabolomics reprogramming in host immunity. The correlation between Bayogenin 3‐O‐Cellobioside levels and blast resistance suggests that engineering saponin expression in cereal crops represents attractive and sustainable disease management. [ABSTRACT FROM AUTHOR]

Summary: Secondary metabolites (SMs) are crucial for fungi and vary in function from beneficial antibiotics to pathogenicity factors. To generate diversified SMs that enable different functions, SM‐coding regions rapidly evolve in fungal genomes. However, the driving force and genetic mechanism of fungal SM diversification in the context of host‐pathogen interactions remain largely unknown. Previously, we grouped field populations of the rice blast fungus Magnaporthe oryzae (syn: Pyricularia oryzae) into three major globally distributed clades based on population genomic analyses. Here, we characterize a recent duplication of an avirulent gene‐containing SM cluster, ACE1, in a clonal M. oryzae population (Clade 2). We demonstrate that the ACE1 cluster is specifically duplicated in Clade 2, a dominant clade in indica rice‐growing areas. With long‐read sequencing, we obtained chromosome‐level genome sequences of four Clade 2 isolates, which displayed differences in genomic organization of the ACE1 duplication process. Comparative genomic analyses suggested that the original ACE1 cluster experienced frequent rearrangement in Clade 2 isolates and revealed that the new ACE1 cluster is located in a newly formed and transposable element‐rich region. Taken together, these results highlight the frequent mutation and expansion of an avirulent gene‐containing SM cluster through transposable element‐mediated whole‐cluster duplication in the context of host‐pathogen interactions. [ABSTRACT FROM AUTHOR]

Background: A number of Pyricularia species are known to infect different grass species. In the case of Pyricularia oryzae (syn. Magnaporthe oryzae), distinct populations are known to be adapted to a wide variety of grass hosts, including rice, wheat and many other grasses. The genome sizes of Pyricularia species are typical for filamentous ascomycete fungi [~ 40 Mbp for P. oryzae, and ~ 45 Mbp for P. grisea]. Genome plasticity, mediated in part by deletions promoted by recombination between repetitive elements [Genome Res 26:1091-1100, 2016, Nat Rev Microbiol 10:417-430,2012] and transposable elements [Annu Rev Phytopathol 55:483-503,2017] contributes to host adaptation. Therefore, comparisons of genome structure of individual species will provide insight into the evolution of host specificity. However, except for the P. oryzae subgroup, little is known about the gene content or genome organization of other Pyricularia species, such as those infecting Pennisetum grasses. Results: Here, we report the genome sequence of P. penniseti strain P1609 isolated from a Pennisetum grass (JUJUNCAO) using PacBio SMRT sequencing technology. Phylogenomic analysis of 28 Magnaporthales species and 5 non-Magnaporthales species indicated that P1609 belongs to a Pyricularia subclade, which is genetically distant from P. oryzae. Comparative genomic analysis revealed that the pathogenicity-related gene repertoires had diverged between P1609 and the P. oryzae strain 70–15, including the known avirulence genes, other putative secreted proteins, as well as some other predicted Pathogen-Host Interaction (PHI) genes. Genomic sequence comparison also identified many genomic rearrangements relative to P. oryzae. Conclusion: Our results suggested that the genomic sequence of the P. penniseti P1609 could be a useful resource for the genetic study of the Pennisetum-infecting Pyricularia species and provide new insight into evolution of pathogen genomes during host adaptation. [ABSTRACT FROM AUTHOR]

The mevalonate pathway is an efficient biosynthesis pathway that yields isoprenoids for promoting different crucial cellular functions, including ergosterol synthesis and growth regulation. Acetoacetyl-CoA acetyltransferase (EC2.3.1.9) is the first major catalytic enzyme constituting the mevalonate pathway and catalyzes the transformation of Acetoacetyl-CoA from two molecules of acetyl-CoA enroute ergosterol production in fungi. We identified two homologous genes encoding Acetoacetyl-CoA acetyltransferase (MoAcat1 and MoAcat2) in Magnaporthe oryzae , the rice blast fungus. Phylogenetic analysis indicates these two genes have different evolutionary history. We subsequently, conducted targeted gene deletion using homologous recombination technology to ascertain the unique roles of the two MoAcat homologues during the fungal morphogenesis and pathogenesis. The findings from our investigations showed that the activity of MoAcat1 promoted virulence in the rice blast fungus as such, the ΔMoacat1 mutants generated exhibited defect in virulence, whilst ΔMoacat1 mutants did not portray growth defects. ΔMoacat2 mutants on the other hand were characterized by reduction in growth and virulence. Furthermore, MoAcat1 and MoAcat2 showed different expression patterns and subcellular localizations in M. oryzae . From our investigations we came to the conclusion that, different subcellular localization contributes to the diverse functions of MoAcat1 and MoAcat2, which helps the successful establishment of blast disease by promoting efficient development of cell morphology and effective colonization of host tissue. [ABSTRACT FROM AUTHOR]

Highlights: [•] Magnaporthe oryzae encodes eight putative RhoGAP proteins. [•] MoRga1 regulates conidial morphology and appressorial formation. [•] MoLrg1 is required for conidiogenesis, vegetative growth and pathogenicity. [•] Both MoRga1 and MoLrg1 interact with MoRac1 and MoCdc42. [•] LIM domain, RhoGAP domain and Arginine 1032 are all essential for MoRga1 function. [ABSTRACT FROM AUTHOR]

• Carbon catabolite repressor MoCreA can shuttle between nucleus and cytoplasm in M. oryzae. • MoCreA plays a vital role in precise regulation of the asexual development. • MoCreA was required for pathogenicity of the rice blast fungus. • Disruption of MoCreA resulted in the extensive gene expression variations. During the infection and colonization process, the rice blast fungus Magnaporthe oryzae faces various challenges from hostile environment, such as nutrient limitation and carbon stress, while carbon catabolite repression (CCR) mechanism would facilitate the fungus to shrewdly and efficiently utilize carbon nutrients under fickle nutritional conditions since it ensures the preferential utilization of most preferred carbon sources through repressing the expression of enzymes required for the utilization of less preferred carbon sources. Researches on M. oryzae CCR have made some progress, however the involved regulation mechanism is still largely obscured, especially, little is known about the key carbon catabolite repressor CreA. Here we identified and characterized the biological functions of the CreA homolog MoCreA in M. oryzae. MoCreA is constitutively expressed throughout all the life stages of the fungus, and it can shuttle between nucleus and cytoplasm which is induced by glucose. Following functional analyses of MoCreA suggested that it was required for the vegetative growth, conidiation, appressorium formation and pathogenicity of M. oryzae. Moreover, comparative transcriptomic analysis revealed that disruption of MoCreA resulted in the extensive gene expression variations, including a large number of carbon metabolism enzymes, transcription factors and pathogenicity-related genes. Taken together, our results demonstrated that, as a key regulator of CCR, MoCreA plays a vital role in precise regulation of the asexual development and pathogenicity of the rice blast fungus. [ABSTRACT FROM AUTHOR]