MoSep3 and MoExo70 are needed for MoCK2 ring assembly essential for appressorium function in the rice blast fungus,...

Polar growth during appressorium formation is vital for the penetration peg formation in the rice blast fungus, Magnaporthe oryzae. Previous research has shown that the Sln1-septin-exocyst complex, localized at the base of the appressorium in contact with the leaf surface, forms a ring structure that influences growth polarity and affects penetration peg formation, and is necessary for pathogenicity. Our previous research showed CK2 proteins assemble another ring structure positioned perpendicular to the Sln1-septin-exocyst complex. Our research showed that the CK2 ring needs to become correctly assembled for penetration peg function and subsequent plant infection. In the present study, we found that the ring structures of CK2 are absent in the appressorium of ΔMoSep3 septin deletion mutants lacking the septin ring of the Sln1-septin-exocyst complex. Sln1 affects the septin proteins that recruit the exocyst complex that localizes as another ring at the appressorium's bottom. Destruction of the exocyst complex by mutation also causes incorrect localization of the CK2 ring structure. In conclusion, CK2 probably takes part in reestablishing the appressorium' spolarity growth necessary for penetration peg formation. We can also conclude that the correct localization and assembly of one or more CK2 ring structures in the appressorium depend on the initial assembly of the Sln1-septin-exocyst complex two rings at the base of the appressorium.