Abstract
The pathogenic life cycle of the rice blast fungus Magnaporthe oryzae involves a series of morphogenetic changes, essential for its ability to cause disease. The smo mutation was identified > 25 years ago, and affects the shape and development of diverse cell types in M. oryzae, including conidia, appressoria, and asci. All attempts to clone the SMO1 gene by map-based cloning or complementation have failed over many years. Here, we report the identification of SMO1 by a combination of bulk segregant analysis and comparative genome analysis. SMO1 encodes a GTPase-activating protein, which regulates Ras signaling during infection-related development. Targeted deletion of SMO1 results in abnormal, nonadherent conidia, impaired in their production of spore tip mucilage. Smo1 mutants also develop smaller appressoria, with a severely reduced capacity to infect rice plants. SMO1 is necessary for the organization of microtubules and for septin-dependent remodeling of the F-actin cytoskeleton at the appressorium pore. Smo1 physically interacts with components of the Ras2 signaling complex, and a range of other signaling and cytoskeletal components, including the four core septins. SMO1 is therefore necessary for the regulation of RAS activation required for conidial morphogenesis and septin-mediated plant infection.
Highlights
MAGNAPORTHE oryzae is an ascomycete fungus responsible for rice blast disease (Zhang et al 2016), a devastating plant disease that results in severe losses to the global rice harvest each year
Whole-genome sequencing of bulked DNA samples identified a region of 2,061,034 bases on supercontig 8.6, which was defined by SNPs showing . 85% linkage to SMO1 using bulked segregant analysis (BSA) (Figure 1A)
We have provided evidence that SMO1 encodes a Ras GTPase-activating protein that plays important functions in cell shape determination and infection-related development in the rice blast fungus
Summary
MAGNAPORTHE oryzae (synonym of Pyricularia oryzae) is an ascomycete fungus responsible for rice blast disease (Zhang et al 2016), a devastating plant disease that results in severe losses to the global rice harvest each year. The rice blast fungus initiates plant infection when a threecelled spore, or conidium, lands and germinates on a leaf surface. The M. oryzae SMO1 locus was first defined from multiple mutants identified spontaneously or through genetic screens that took place more than 25 years ago (Hamer et al 1989b). Wild-type conidia in M. oryzae, by contrast, are bilaterally symmetrical and pyriform (tear-drop) shaped These spore morphology mutants were named Smo and tetrad analysis showed that the phenotype was due to a single gene mutation that defined a new locus, SMO1, involved in cell shape determination. SMO1 is necessary for septinmediated F-actin remodeling at the appressorium pore, and plays a critical role in plant infection by the rice blast fungus
Sign-in/Register to view highlights & summary 
Published Version (
Free)
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 call