A conserved enzyme of smut fungi facilitates cell-to-cell extension in the plant bundle sheath

Smut fungi secrete effector proteins that suppress host plant immunity. Here the authors show that the corn smut effector Erc1 has 1,3-beta-glucanase activity and promotes virulence in maize leaves by attenuating beta-glucan-induced defense responses. Smut fungi comprise one of the largest groups of fungal plant pathogens causing disease in all cereal crops. They directly penetrate host tissues and establish a biotrophic interaction. To do so, smut fungi secrete a wide range of effector proteins, which suppress plant immunity and modulate cellular functions as well as development of the host, thereby determining the pathogen's lifestyle and virulence potential. The conserved effector Erc1 (enzyme required for cell-to-cell extension) contributes to virulence of the corn smut Ustilago maydis in maize leaves but not on the tassel. Erc1 binds to host cell wall components and displays 1,3-beta-glucanase activity, which is required to attenuate beta-glucan-induced defense responses. Here we show that Erc1 has a cell type-specific virulence function, being necessary for fungal cell-to-cell extension in the plant bundle sheath and this function is fully conserved in the Erc1 orthologue of the barley pathogen Ustilago hordei.

Automated summary

The corn smut effector Erc1 has 1,3-beta-glucanase activity and promotes virulence in maize leaves by attenuating beta-glucan-induced defense responses. Smut fungi secrete effector proteins that suppress host plant immunity and modulate cellular functions and development of the host.