Abstract
The appropriate development of conidia and appressoria is critical in the disease cycle of many fungal pathogens, including Magnaporthe oryzae. A total of eight genes (MoHOX1 to MoHOX8) encoding putative homeobox transcription factors (TFs) were identified from the M. oryzae genome. Knockout mutants for each MoHOX gene were obtained via homology-dependent gene replacement. Two mutants, ΔMohox3 and ΔMohox5, exhibited no difference to wild-type in growth, conidiation, conidium size, conidial germination, appressorium formation, and pathogenicity. However, the ΔMohox1 showed a dramatic reduction in hyphal growth and increase in melanin pigmentation, compared to those in wild-type. ΔMohox4 and ΔMohox6 showed significantly reduced conidium size and hyphal growth, respectively. ΔMohox8 formed normal appressoria, but failed in pathogenicity, probably due to defects in the development of penetration peg and invasive growth. It is most notable that asexual reproduction was completely abolished in ΔMohox2, in which no conidia formed. ΔMohox2 was still pathogenic through hypha-driven appressoria in a manner similar to that of the wild-type. However, ΔMohox7 was unable to form appressoria either on conidial germ tubes, or at hyphal tips, being non-pathogenic. These factors indicate that M. oryzae is able to cause foliar disease via hyphal appressorium-mediated penetration, and MoHOX7 is mutually required to drive appressorium formation from hyphae and germ tubes. Transcriptional analyses suggest that the functioning of M. oryzae homeobox TFs is mediated through the regulation of gene expression and is affected by cAMP and Ca2+ signaling and/or MAPK pathways. The divergent roles of this gene set may help reveal how the genome and regulatory pathways evolved within the rice blast pathogen and close relatives.
Highlights
Magnaporthe oryzae is an ascomycete fungus and the causal agent of rice blast, the most destructive disease of rice worldwide
To elucidate molecular mechanisms in asexual reproduction and appressorium-mediated disease development, we identified eight homeobox transcription factors through a genome-wide in silico analysis
Characterization using deletion mutants revealed that each homeobox transcription factors (TFs) functions as a stage-specific regulator for conidial shape, hyphal growth, conidiation, appressorium development, and invasive growth during M. oryzae development
Summary
Magnaporthe oryzae is an ascomycete fungus and the causal agent of rice blast, the most destructive disease of rice worldwide. The conidia attach to the surface of host plants upon hydration and produce germ tubes This fungus develops a specialized infection structure, an appressorium, at the tip of the germ tube. The fungus develops invasive hyphae, colonizes host cells, and produces massive conidia via conidiogenesis, serving as secondary inocula for new infections. This infection cycle may occur many times during the growing season, resulting in explosive disease development. Understanding the molecular mechanisms involved in conidiation and appressorium development is a prerequisite to provide novel strategies for disease management
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
