A Homeobox Gene Is Essential for Conidiogenesis of the Rice Blast Fungus Magnaporthe oryzae

Abstract

Magnaporthe oryzae starts its infection by the attachment of pyriform conidia on rice tissues, and severity of the disease epidemic is proportional to the quantity of conidia produced in the rice blast lesions. However, the mechanism of conidial production is not well understood. Homeodomain proteins play critical roles in regulating various growth and developmental processes in fungi and other eukaryotes. Through targeted gene replacement, we find that deletion of HTF1, one of seven homeobox genes in the fungal genome, does not affect mycelial growth but causes total defect of conidial production. Further observation revealed that the Deltahtf1 mutant produces significantly more conidiophores, which curve slightly near the tip but could not develop sterigmata-like structures. Although the Deltahtf1 mutant fails to form conidia, it could still develop melanized appressoria from hyphal tips and infect plants. The expression level of HTF1 is significantly reduced in the Deltamgb1 G-beta and DeltacpkA deletion mutant, and the ACR1 but not CON7 gene that encodes transcription factor required for normal conidiogenesis is significantly downregulated in the Deltahtf1 mutant. These data suggest that the HTF1 gene is essential for conidiogenesis, and may be functionally related to the trimeric G-protein signaling and other transcriptional regulators that are known to be important for conidiation in M. oryzae.

CtPMK1, a mitogen‐activated‐protein kinase gene, is required for conidiation, appressorium formation, and pathogenicity of Colletotrichum truncatum on soybean

“…The hyphopodia in M. oryzae have been well characterised (Kong et al, 2013). In addition, the function of the Pmk1 pathway in regulating the differentiation of hyphopodia on hyphal tips is conserved (Liu et al, 2010), which is consistent with our finding that CtPMK1 is essential for hyphopodia formation in C. truncatum. Fig.…”

Screening of a synthetic peptide combinatorial library to identify inhibitors of the appressorium formation in Magnaporthe oryzae

“…3). As previously reported, in addition of melanized appressoria formed at the tip of germ tubes (AP), M. oryzae is able to develop appressorium-like structures at hyphal tips (ALS) [21,22]. In this work, all these structures were observed after 24 h incubation of M. oryzae in the absence or presence of the four peptides (PAF104, MgAPI24, MgAPI40 and MgAPI47).…”

Two Rab5 Homologs Are Essential for the Development and Pathogenicity of the Rice Blast Fungus Magnaporthe oryzae

“…Besides the appressoria developed from conidia, a special structure formed at the tips of hyphae on hydrophobic or plant surfaces, called ALS, can also trigger hyphal infection of susceptible hosts (Sun et al, 2006; Liu et al, 2010; Kong et al, 2013). The hyphae of MoRab5 deficient strains were inoculated on the surface of hydrophobic film (Gelbond film from BMA company, USA), and no ALS emerged in any of the MoRab5:DN and MoRab5:RNAi strains even after 72 hpi, on the contrast, typical ALSs were readily detected at the tips of hyphae in Guy11 after 24 hpi ( Figure 7D ).…”