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Wheat blast is an important disease that affects cross-border food security. The causal pathogen, Pyricularia oryzae (syn. Magnaporthe oryzae) Triticum pathotype (MoT), forms a phylogenetic group distinct from the other P. oryzae pathotypes pathogenic on various gramineous plants. Here we developed MoT-specific primer sets for qPCR and LAMP detection methods, and their amplification specificity and efficiency were tested in comparison with previous reported MoT-specific primers. The amplification efficiency and specificity were affected by the polymerase premix. To evaluate the detection specificity, purified DNA samples of 15 MoT isolates, 89 non-MoT isolates of Pyricularia spp., and crude DNA from wheat plants inoculated with MoT were used. We conclude that the Sp3 primer sets for qPCR and the MoT3L primer sets for LAMP were the best in this research. [ABSTRACT FROM AUTHOR]

We determined the full-length genome sequence of Br48 and compared it with those of rice (70 - 15), finger millet (MZ5-1-6), and ryegrass (LpKY97) strains, for which the full-length genome sequences are available in the public databases. This article is an abstract of the presentation by a winner of the Society Fellowship at the 2023 Annual Meeting of the Phytopathological Society of Japan in Kanagawa (online). Instead, epigenetics involves DNA methylation, histone modifications and non-coding RNA-mediated processes as the molecular basis for gene regulation. When analyzed genome-wide, a significant correlation between a decrease in IPC levels and an increase in H3K27me3 levels was detected, suggesting that there is a relationship between HGT-derived genes and H3K27me3 levels in the Br48 genome, especially in the variable regions. [Extracted from the article]

Horizontal gene transfer (HGT) is a means of exchanging genetic material asexually. The process by which horizontally transferred genes are domesticated by the host genome is of great interest but is not well understood. In this study, we determined the telomere-to-telomere genome sequence of the wheat-infecting Pyricularia oryzae strain Br48. SNP analysis indicated that the Br48 strain is a hybrid of wheat- and Brachiaria -infecting strains by a sexual or parasexual cross. Comparative genomic analysis identified several megabase-scale "insertions" in the Br48 genome, some of which were possibly gained by HGT-related events from related species, such as P. pennisetigena or P. grisea. Notably, the mega-insertions often contained genes whose phylogeny is not congruent with the species phylogeny. Moreover, some of the genes have a close homolog even in distantly related organisms, such as basidiomycetes or prokaryotes, implying the involvement of multiple HGT events. Interestingly, the levels of the silent epigenetic marks H3K9me3 and H3K27me3 in a genomic region tended to be negatively correlated with the phylogenetic concordance of genes in the same region, suggesting that horizontally transferred DNA is preferentially targeted for epigenetic silencing. Indeed, the putative HGT-derived genes were activated when MoKmt6 , the gene responsible for H3K27me3 modification, was deleted. Notably, these genes also tended to be up-regulated during infection, suggesting that they are now under host control and have contributed to establishing a fungal niche. In conclusion, this study suggests that epigenetic modifications have played an important role in the domestication of HGT-derived genes in the P. oryzae genome. [ABSTRACT FROM AUTHOR]

Pyricularia oryzae and Pyricularia grisea are pathogens that cause blast disease in various monocots. It has been reported that P. oryzae infects the leaves and roots of rice via different mechanisms. However, it is unclear to what extent the tissue types affect the host specificities of P. oryzae and P. grisea. Here, we evaluated the tissue‐specific infection strategies of P. oryzae and P. grisea in various gramineous plants. Generally, mycelial plug inoculation caused root browning but the degree of browning did not simply follow the disease index on leaves. Interestingly, the Triticum and Digitaria pathotypes caused strong root growth inhibition in rice, wheat, and barley. Moreover, the Digitaria pathotype inhibited root branching only in rice. Culture filtrate reproduced these inhibitory effects on root, suggesting that some secreted molecules are responsible for the inhibitions. Observation of root sections revealed that most of the infection hyphae penetrated intercellular spaces and further extended into root cells, regardless of pathotype and host plant. The infection hyphae of Digitaria and Triticum pathotypes tended to localize in the outer layer of rice roots, but not in those of wheat and barley roots. The infection hyphae of the Oryza pathotype were distributed in both the intercellular and intracellular spaces of rice root cells. Pathogenesis‐related genes and reactive oxygen species accumulation were induced after root inoculation with all combinations. These results suggest that resistance reactions were induced in the roots of gramineous plants against the infection with Pyricularia isolates but failed to prevent fungal invasion. [ABSTRACT FROM AUTHOR]

Transposable elements are common targets for transcriptional and post-transcriptional gene silencing in eukaryotic genomes. However, the molecular mechanisms responsible for sensing such repeated sequences in the genome remain largely unknown. Here, we show that machinery of homologous recombination (HR) and RNA silencing play cooperative roles in copy number-dependent de novo DNA methylation of the retrotransposon MAGGY in the fungus Pyricularia oryzae. Genetic and physical interaction studies revealed that RecA domain-containing proteins, including P. oryzae homologs of Rad51, Rad55, and Rad57, together with an uncharacterized protein, Ddnm1, form complex(es) and mediate either the overall level or the copy number-dependence of de novo MAGGY DNA methylation, likely in conjunction with DNA repair. Interestingly, P. oryzae mutants of specific RNA silencing components (MoDCL1 and MoAGO2) were impaired in copy number-dependence of MAGGY methylation. Co-immunoprecipitation of MoAGO2 and HR components suggested a physical interaction between the HR and RNA silencing machinery in the process. Ba Van Vu, Quyet Nguyen et al. investigate the mechanism by which transposable elements are targeted for DNA methylation, using the fungus Pyricularia oryzae as a model system. They find that copy number-dependent DNA methylation and thus silencing of the MAGGY retrotransposon requires cooperative action of homologous recombination and RNA silencing machinery. [ABSTRACT FROM AUTHOR]

Here we addressed the involvement of histone methylation at H3 lysine 4 (H3K4me) in substrate-dependent activation of cell-wall-degrading enzymes (CWDEs) in Magnaporthe oryzae. Transcriptional activation of 36 putative CWDEs including cellobiohydrolases, endoglucanases, β-glucosidases, and endoxylanases was assessed by qRT-PCR. Among the CWDE genes, 16 were upregulated during infection and also in media containing their respective substrates with an exception. Interestingly, the substrate-dependent activation of most CWDE genes was severely impaired in a deletion mutant of MoSET1, histone H3K4 methyltransferase in M. oryzae, suggesting that MoSET1 directly or indirectly regulates a wide range of CWDE genes. [ABSTRACT FROM AUTHOR]

Here we report a novel system to induce RNA silencing in Magnaporthe oryzae using the retrotransposon MAGGY. The gene-silencing vector pSilent-MG carries a MAGGY variant with a unique cloning site in the 3′ UTR region and a geneticin-resistance cassette as a selection marker. A gene-silencing assay with a GFP gene revealed that pSilent-MG vectors induced gene silencing at a practical level. In the resulting GFP-silenced transformants, GFP siRNAs accumulated and DNA methylation increased in the GFP-expressing gene, implying that the vector could induce both transcriptional and post-transcriptional gene silencing. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated the induction of cell death, chlorosis, and reactive oxygen species (ROS) generation by Mag-toxin obtained from Pyricularia oryzae. It states that the toxin induced chlorosis on segments of oat leaf incubated in the light. It says that the ROS generation cellular localization induced by the treatment of the toxin was correlated with mitochondria's location. It notes that induction of cell death and ROS generation by the toxin was light-dependent.

Rwt4 (synonym of Rmg1), a temperature-insensitive gene for resistance to Avena isolates of Magnaporthe oryzae, was identified in wheat cultivar Norin 4 in a seedling assay. The significance of Rwt4 was evaluated using flag leaves of wheat cultivars. At high temperature, Norin 4 was completely resistant to Avena isolate Br58, while Chinese Spring, a noncarrier of Rwt4, was susceptible. Genetic analysis of F2 plants derived from Norin 4 × Chinese Spring indicated that the resistance of flag leaves of Norin 4 to the Avena isolate is conditioned by a single major gene. Segregation analysis of F3 seedlings derived from the F2 plants showed that the major gene is actually Rwt4. These results suggest that Rwt4 is effective against Avena isolates throughout the growth stages. Furthermore, screening of Pyricularia isolates from various hosts suggested that Panicum isolates are possible carriers of the corresponding avirulence gene, PWT4. Segregation analyses of F2 and F3 seedlings showed that Panicum isolates actually carry PWT4, and, therefore, that Rwt4 is also effective against Panicum isolates. On the other hand, none of the Oryza, Setaria, Triticum, and Lolium isolates tested was a carrier of PWT4. The significance of this finding is discussed from the viewpoint of epidemics of blast disease on wheat. [ABSTRACT FROM AUTHOR]

Three ourmia-like viruses, designated P yricularia o ryzae o urmia- l ike v irus (PoOLV) 1 to 3, were identified in a wheat-infecting isolate of P. oryzae. The sizes of the full-length PoOLV1-3 genomes were determined to be 2,528, 1,671, and 2,557 nt. Interestingly, we also found two abundant single-stranded RNAs sharing their 5' terminal 25 and 255 nt with PoOLV1 RNA and PoOLV3 RNA, respectively. The PoOLV1- and PoOLV3-associated RNAs (ARNA1 and ARNA3) were 639 and 514 nt in length, and possessed one and two small ORFs, respectively. In the field isolates of P. oryzae , PoOLVs and ARNAs were detectable at varying levels, and the levels of PoOLV1 and ARNA1 as well as those of PoOLV3 and ARNA3, were tightly correlated. In addition, gene silencing of PoOLV1 and PoOLV3 resulted in a reduction of ARNA1 and ARNA3, respectively. There results indicated that replication of ARNA1 and ARNA3 was associated with PoOLV1 and PoOLV3, respectively. [ABSTRACT FROM AUTHOR]