Genomic organization and sequence dynamics of the AvrPiz-t locus in Magnaporthe oryzae

Abstract

Abstract:Plants utilize multiple layers of defense mechanisms to fight against the invasion of diverse pathogens. The R gene mediates resistance, in most cases, dependent on the co-existence of its cognate pathogen-derived avirulence (Avr) gene. The rice blast R gene Piz-t corresponds in gene-for-gene fashion to the Magnaporthe oryzae Avr gene AvrPiz-t. In this study, we determined and compared the genomic sequences surrounding the AvrPiz-t gene in both avirulent and virulent isolates, designating as AvrPiz-t-ZB15 and avrPiz-t-70-15 regions, respectively. The sequence of the AvrPiz-t-ZB15 region is 120 966 bp whereas avrPiz-t-70-15 is 146 292 bp in length. The extreme sequence similarity and good synteny in gene order and content along with the absence of two predicted genes in the avrPiz-t-70-15 region were observed in the predicted protein-coding regions in the AvrPiz-t locus. Nevertheless, frequent presence/absence and highly dynamic organization of transposable elements (TEs) were identified, representing the major variation of the AvrPiz-t locus between different isolates. Moreover, TEs constitute 27.3% and 43.2% of the genomic contents of the AvrPiz-t-ZB15 and avrPiz-t-70-15 regions, respectively, indicating that TEs contribute largely to the organization and evolution of AvrPiz-t locus. The findings of this study suggest that M. oryzae could benefit in an evolutionary sense from the presence of active TEs in genes conferring avirulence and provide an ability to rapidly change and thus to overcome host R genes.

Comparative genomics identifies the Magnaporthe oryzae avirulence effector AvrPi9 that triggers Pi9‐mediated blast resistance in rice

“…It is reasonable to speculate that the centromere‐proximal region could be relatively more stable than the plastic regions where avirulence genes are more commonly found. Contrary to a high frequency of sequence deletions spanning several avirulence genes, for example, AvrLM1 in L. maculans and AvrPita in M. oryzae (Van de Wouw et al ., ; Chuma et al ., ), TE insertion, rather than deletion, in AvrPiz‐t was frequently observed in virulent isolates (Li et al ., ). In this study, we demonstrated that AvrPi9 was present universally in field isolates in both the Philippines and China.…”

Sequence Variation and Recognition Specificity of the Avirulence Gene AvrPiz-T in Magnaporthe Oryzae Field Populations

“…The AvrPiz-t gene resides in a region that comprises high transposable element density on chromosome 7 [43]. It was further identified that a Pot3 transposable element inserted in the 500 bp upstream region in the virulent isolate GUY11 compared to the avirulent isolate KJ201 [27]. In this study, the fact that more diversity has been identified in the promoter region of the AvrPiz-t locus compared to its coding region suggests the function of this gene in a population may be affected from the present/absent polymorphism of transposable element more often than from variation in its coding sequence.…”

“…In M. oryzae strain GUY11, a virulence strain to Piz-t containing cultivar, AvrPiz-t was found present but having a transposable element Pot3 inserted in its promoter region [8]. In the 146 kb AvrPiz-t locus of the strain 70-15 which is derived from GUY11, TEs sequences were also found for as much as 43.2% of the genomic content at this locus, suggesting the dynamic evolution in this region [27].…”

In vitro Expression, Characterisation and Subcellular Localisation of AvrPi54 Protein, an Effector of Rice Blast Fungus <em>Magnaporthe oryzae</em>

“…NMR spectroscopy has revealed that AvrPiz-t contains a β-sandwich comprised of six strands and a Cys62Cys75 disulfide linkage and two other cysteine residues, Cys23 and Cys70 are present on the β1 sheet and loop 4, respectively [49]. It has also been reported earlier that the avirulence of AvrPiz-t is quashed if mutation occurs at a single residue out of the four cysteine residues [50]. Another feature of AvrPi54 protein is hydrophobicity which is found in some proteins like hydrophobins, found in fungi, which function in pathogenicity [51].…”