Polar Growth in the Infectious Hyphae of the PhytopathogenUstilago maydisDepends on a Virulence-Specific Cyclin

Abstract

The maize smut fungus Ustilago maydis switches from yeast to hyphal growth to infect maize (Zea mays) plants. This switching is promoted by mating of compatible cells and seems to be required for plant penetration. Although many genes distinctively expressed during this dimorphic switch have been identified and shown to be essential for the infection process, none seems to be explicitly required for polar growth control. Here, we report the characterization of pcl12, encoding a cyclin that interacts specifically with Cdk5, an essential cyclin-dependent kinase with regulatory roles in morphogenesis in U. maydis. Pcl12 fulfills the requirements to be a virulence-specific regulator of polar growth in U. maydis. First, pcl12 expression is induced during the pathogenic development. Secondly, Pcl12 is sufficient to induce hyperpolarized growth in U. maydis cells, as haploid cells overexpressing pcl12 in axenic conditions produce filaments that were morphologically indistinguishable from those produced during the infection process. Finally, cells defective in pcl12 showed impaired polar growth during the formation of the b-dependent filament, the induction of the conjugation tubes, or the formation of a promycelium in spore germination. However, in spite of this pivotal role during morphogenesis, pcl12 mutants were virulent. We discuss the implications of these results for the role of polar growth during the infection process.

Identification of genes involved in the phosphate metabolism in Cryptococcus neoformans

“…In A. nidulans, the orthologues of ScPho85, An-PhoA and An-PhoB, are essential and play a role in development but not in phosphate acquisition (Bussink and Osmani, 1998;Dou et al, 2003). In Ustilago maydis, UmPHO85 (UnCDK5) is also essential and is shown to function in polarity maintenance and virulence but not in phosphate acquisition (Castillo-Lluva et al, 2007;Flor-Parra et al, 2007). Although we showed that CnPho85 (and CnPho80) is involved in the regulation of the CnPHO system (Figs.…”

The DNA Damage Response Signaling Cascade Regulates Proliferation of the Phytopathogenic FungusUstilago maydisin Planta

“…maydis strains are listed in Table 1. Manipulations with U. maydis, culture methods, gene disruption and gene transfer procedures, survival after DNA damage, and plant infections have been described previously (Castillo-Lluva and Pé rez-Martín, 2005;Flor-Parra et al, 2007;Mielnichuk and Pé rez-Martín, 2008;Mielnichuk et al, 2009). Protein extracts, immunoprecipitations, and immunoblot analysis were performed as described previously (García-Muse et al, 2004;Sgarlata and Pé rez-Martín, 2005).…”

A role for the DNA-damage checkpoint kinase Chk1 in the virulence program of the fungusUstilago maydis

“…Plant infection and charcoal assays were described previously (Flor-Parra et al, 2007). Staining of infected plant samples with Chlorazole Black E was done as described previously (Brachmann et al, 2003).…”

“…Which mechanisms are used by the bW-bE heterodimer to induce the hyperpolarized growth and to arrest the cell cycle in the infectious hypha and at which stage this occurs are unknown, but these issues are currently being studied. For example, recent results from our laboratory indicated that the activation of hyperpolarized growth after bW-bE heterodimer formation is dependent on the U. maydis ortholog of the cyclin-dependent kinase Cdk5, a well-known regulator of neuron development in mammals (Alvarez-Tabares and Perez-Martin, 2008;Castillo-Lluva et al, 2007;Flor-Parra et al, 2007).…”