Exploring the role of PTN1 in ustilago maydis.

Abstract

Signal transduction is a key aspect of biological life. PTEN (phosphatase and tensin homolog) is a widely studied signaling protein in mammalian systems, where it acts as a tumor suppressor. Numerous studies have conclusively demonstrated the anti-cancerous effect of this protein. Mutations in the PTEN gene have been implicated in several disorders including cancer, diabetes, and Cowden syndrome, among others. It is part of the PI3K-PTEN-AKT-mTOR signaling pathway and is responsible for various metabolic and cellular activities. This pathway is found to be conserved across several eukaryotic systems including yeast, Drosophila melanogaster and Caenorhabditis elegans. While PTEN orthologues have been characterized in ascomycete fungi, it has not been reported in any basidiomycete fungi. The initial part of the current study was aimed at the characterization of PTEN orthologue, ptn1, of Ustilago maydis, a basidiomycete fungus. When the U. maydis, ptn1 gene was either deleted or overexpressed, it was found that the deletion of this gene lead to reduced virulence, spore production, and germination rate; effects of the overexpression were more subtle or not discernable. Previous studies have indicated that two other signaling proteins, Rho1 and Pdc1, are physical interactors of Ptn1. The goal of the latter part of the present study was to explore the functional interaction of Ptn1 with vi Rho1 and Pdc1. Our experiments indicated a functional connection between these genes, especially in processes that are related to stress tolerance, cellular morphology, and virulence of the fungus, suggesting that they may be elements of the same regulatory pathway. We predict that the pdc1 interaction with ptn1 may be the reverse of that of rho1 with ptn1. In addition, our experiments with an orthologue of S6K1, aga1, showed that its deletion leads to some of the same phenotypes seen with that of ptn1, pdc1 and/or rho1. The current phenotypes of these mutant strains when considered in the context of already available information about the role of these genes in other systems indicate that they may be part of a pathway that modulates cytoskeletal rearrangements. vii