The core effector Cce1 is required for early infection of Ustilago maydis

The biotrophic pathogen Ustilago maydis is the causative agent of corn smut disease, infecting one of the most important crops worldwide – Zea mays¹. During the infection process, tumor formation is induced in plant tissues. To successfully colonize its host plant, U. maydis secretes proteins that suppress plant defense responses and facilitate the establishment of biotrophy. These proteins are termed effectors, and among these some belong to a set of highly conserved effectors that are ultimately necessary to establish a successful biotrophic interaction². In this work, we describe the U. maydis effector protein Cce1 (Cysteine-rich core effector 1). This protein is essential for the virulence of the fungus. Cce1 is upregulated during infection and is secreted from the fungal hyphae. Δcce1 mutant strains are blocked at early stages of infection and induce callose deposition as a result of plant defense responses. In the genome of other smut fungi highly conserved orthologs of Cce1 can be found. Complementation experiments using an ortholog derived from U. bromivora was successful and could re-establish the virulence of the SG200Δcce1 deletion strain.

These data indicate that it is likely that Cce1 belongs to the set of core effectors, which are absolutely needed for establishment of a successful infection.

References:

1| Martínez-Espinoza, A. D., García-Pedrajas, M. D., and Gold, S. E. 2002. The Ustilaginales as plant pests and model systems. Fungal Genetics and Biology 35, 1–20.

2| Brefort T., Doehlemann G., Mendoza-Mendoza A., Reissmann S., Djamei A., and Kahmann R. 2009. Ustilago maydis as a pathogen. Annual Review of Phytopathology Vol. 47:423-445