A kelch domain cell end protein, PoTea1, mediates cell polarization during appressorium morphogenesis in Pyricularia...

The rice blast fungus Pyricularia oryzae differentiates into an infection structure, called an appressorium, for plant penetration. The process of appressorium formation requires the transformation of polarized growth to isotropic growth, while penetration requires the opposite growth transformation from isotropic to polarized. Polarized growth requires coordinated organization of cytoskeletal elements, such as microtubule and actin. We identified PoTea1, a homolog of Tea1 from Schizosaccharomyces pombe, and characterized its roles in P. oryzae. After PoTEA1 deletion, ∆Potea1 displayed slowed hyphal growth, decreased sporulation, increased hyphal branches, abnormal two-celled spores, and reduced plant penetration and virulence. During appressorium formation, ∆Potea1 developed a long germ tube with a small appressorium, leading to delayed appressorium differentiation and reduced glycogen and lipid droplet degradation. ∆Potea1 is defective in cAMP-PKA and Pmk1 MAPK pathways. PoTea1 localized at hyphal tips and appressoria as bright dots and was highly dynamic during appressorium formation. PoTea1 formed a complex with itself by self-assembly that was highly dependent on its kelch motif. The coiled-coil motif C2 of PoTea1 is involved in self polymerization and appressorium formation. Benomyl and latrunculin A, two cytoskeleton inhibitors, disturbed the stable localization of PoTea1 at vegetative hyphal tips. We speculate that PoTea1 functions in appressorium formation and virulence by mediating cell polarity in P. oryzae.