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Magnaporthe appressoria: wt vs. bip1 deletion mutant

ABSTRACT: The identification of genes regulated by the transcription factor Bip1 during appressorial development. The rice blast fungus Magnaporthe grisea develops melanized appressoria with high turgor pressure that inject the fungus into epidermal host cells. A screen for M. grisea non-pathogenic mutants recovered mutant M763 with reduced penetration efficiency and infectious growth. Complementation analysis identified a gene inactivated in M763 that encodes a novel basic leucine zipper (bZIP) transcription factor named Bip1 (B-ZIP Involved in Pathogenesis1). Deletion of Bip1 by targeted replacement generated non-pathogenic mutants that are unable to infect rice or barley. These mutants develop melanized appressoria that are unable to penetrate intact or wounded host leaves. Bip1 mRNA was detected in fungal spores, appressoria and infected leaves but not in mycelia, while a BIP1:GFP fusion was detected only in nuclei of mature appressoria. Genome wide transcriptome analysis identified 44 genes down regulated in Δbip1:hph appressoria. Most of these genes (77%) are specifically expressed in appressoria and encode enzymes involved in secondary metabolism (11), secreted proteins and enzymes (18) and G-Protein Coupled Receptors (GPCRs) (5). Promoters of BIP1 down-regulated genes share a similar GCN4/bZIP DNA binding motif (TGACTC). Gel shift assays showed that the motifs from 6 of the 7 promoters tested bind to recombinant BIP1 in vitro, including MGG_08381.5 from the ACE1 locus. Mutation of BIP1 binding sites in the MGG_08381.5 promoter significantly reduced its appressorium specific expression. Molecular and biochemical studies confirmed that BIP1 controls the expression of a distinct set of M. grisea genes in the appressorium, revealing a novel regulatory network involved in early stages of fungal infection that activates a diverse gene expression program resulting in a “shock and awe” impact on the plant host.

ORGANISM(S): Pyricularia grisea

PROVIDER: GSE18823 | GEO | 2018/01/05

SECONDARY ACCESSION(S): PRJNA121151

REPOSITORIES: GEO

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Project description:Colletotrichum graminicola is a hemibiotrophic fungal pathogen that causes maize anthracnose disease. It progresses through three recognizable phases of pathogenic development *in planta*: melanized appressoria that form on the host surface prior to penetration; biotrophy, characterized by colonization of living host cells; and necrotrophy, characterized by host cell death and symptom development. An improved filtering algorithm and a Mixed Effects Generalized Linear Model (GLM) were developed and applied to an existing Illumina transcriptome dataset, substantially increasing the statistical power of the analysis of *C. graminicola* gene expression during infection and colonization. Additionally, the *in planta* transcriptome of the wild-type was compared with that of a mutant strain impaired in the establishment of biotrophy, allowing detailed dissection of events occurring specifically during penetration, and during early versus late biotrophy. Results indicated that there is a continuum of activities that occur during colonization of maize by *C. graminicola*, and that boundaries drawn between the three recognizable phases are artificial. More than 2000 fungal genes were differentially transcribed in waves during appressorial maturation, penetration, and colonization. Secreted proteins and membrane receptors were over-represented among the differentially expressed genes, suggesting that the fungus engages in an intimate and dynamic conversation with the host, beginning prior to penetration. This communication process is likely to involve reception of plant signals that trigger subsequent developmental progress in the fungus, as well as the production of signals that induce responses in the host. Later phases of biotrophy were more similar to necrotrophy, with increased production of secreted proteases, inducers of plant cell death, hydrolases, and membrane bound transporters for the uptake and egress of potential toxins, signals, and nutrients. The differentially expressed genes could be used as landmarks to more accurately identify developmental progress in compatible versus incompatible interactions involving genetic variants of both host and pathogen.

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Magnaporthe appressoria: wt vs. bip1 deletion mutant

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