The Risk of Wheat Blast in Rice-Wheat Co-Planting Regions in China: MoO Strains of Pyricularia oryzae Cause Typical Symptom and Host Reaction on Both Wheat Leaves and Spikes.

The Triticum pathotype of Magnaporthe oryzae (syn. Pyricularia oryzae) causes wheat blast, which has recently spread to Asia. To assess the potential risk of wheat blast in rice-wheat growing regions, we investigated the pathogenicity of 14 isolates of P. oryzae on 32 wheat cultivars, among which Oryzae pathotype of P. oryzae (MoO) isolates were completely avirulent on the wheat cultivars at 22°C but caused various degrees of infection 25°C. These reactions at 25°C were isolate and cultivar dependent, like race-cultivar specificity, which was also recognized at the heading stage and caused typical blast symptoms on spikes. Microscopic analyses indicated that a compatible MoO isolate produced appressoria and infection hyphae on wheat as on rice. When we compared transcriptomes in wheat-MoO interactions, the bulk of pathogen-related genes were upregulated or downregulated in compatible and incompatible patterns, but changes in gene transcription were more significant in a compatible pattern. These results indicate that temperature could influence the infection ratio of wheat with MoO, and some MoO strains could be potential pathogens that increase the risk of wheat blast outbreaks in wheat-rice growing regions with global warming. In addition, certain wheat cultivars exhibited resistance and are assumed to carry resistance-promoting genes to the MoO strains.

Dual screening for targeted gene replacement mutant in Magnaporthe oryzae with GUS as negative marker / 生物工程学报

To improve the efficiency of targeted gene replacement (TGR), a dual screen (DS) system with gusA gene as negative selective marker (GUS-DS) was developed in Magnaporthe oryzae. First, we tested the endogenous beta-glucuronidase (GUS) activities of 78 fungal strains. All tested strains were GUS-, only with 3 exceptions. Whereas, after the gusA being introduced in, M. oryzae, Fusarium oxysporum and Colletotrichum lagenarium acquired high GUS activities. The gusA is thus usable as a selective maker in fungal species. With gusA as the negative marker, HPH gene as the positive marker, and the peroxisomal targeting signal receptor genes MGPEX5 and MGPEX7 as 2 instances of target genes, we established the GUS-DS system. After transformation, we collected the transformants from hygromycin B screen media and then tested the GUS activities of them. The GUS- ones were selected as potential mutants and checked in succession by PCR and Southern blotting to identify the true mutants and calculate the efficiency of GUS-DS. As a result, GUS-DS improved the screen efficiency for delta mgpex5 from 65.8% to 90.6%, and for delta mgpex7 from 31.2% to 82.8%. In addition, we established a multiple PCR (M-PCR) method for mutant confirmation. By amplifying the different regions at the targeted locus, M-PCR differentiated the wild type, the ectopic transformants and the mutants effectively and rapidly, and had the same reliability as Southern blotting. In conclusion, GUS-DS and M-PCR are useful tools to improve the efficiency of TGR and would be helpful for fungal genomics.