Arabidopsis Infection by Haploid or Diploid Strains of Ustilago maydis Reveals its Capacity as A Necrotrophic or Biotrophic Phytopathogen

Abstract

The use of experimental patho-systems is a widely used strategy for understanding the pathogenic processes developed by many infectious agents. Ustilago maydis is a Basidiomycota fungus that naturally infects only maize and teozintle. We have established that under axenic conditions, either haploid or diploid strains of U. maydis can infect Arabidopsis thaliana, and in this work we analyzed the different behaviour of U. maydis haploid, diploid, and merodiploid strains in the mating genes during Arabidopsis infection. We determined the severity of infection, cell death, and the production of phytohormones and reactive oxygen species (ROS), occurring in the invaded host. Our results indicate that whereas U. maydis diploid and merodiploid strains behave as biotrophic parasites, the behaviour of the haploid strain is necrotrophic. We suggest that this difference resides in the fact that only the former two strains, but not the haploid one, are able to synthesize the master regulator of the biotrophic pathogenic behaviour, the bE/bW heterodimer encoded by the b genes of the two mating partners.