Sustained cell polarity and virulence in the phytopathogenic fungusUstilago maydisdepends on an essential cyclin-dependent kinase from the Cdk5/Pho85 family

Abstract

Cyclin-dependent kinases from the Cdk5/Pho85 family are thought to play important roles in morphogenesis in organisms as diverse as yeast and humans. Here we used the corn smut fungus Ustilago maydis to address the role of Cdk5/Pho85 kinases in the morphogenesis and virulence of dimorphic phytopathogens. We found that Cdk5 is essential for growth in U. maydis. A temperature-sensitive cdk5 mutant caused cell wall and morphology defects at the restrictive temperature. Actin patches labeled with a fimbrin-GFP fusion protein were delocalized and a GFP-Myo5 fusion was directed towards the growing cell pole and rapidly dissociated from the tip. These defects were found to be due to an impairment in the maintenance of cell polarity. Our results indicated that Cdk5 is required for the activity of Rac1, probably at the level of the localization of its GEF, Cdc24. Cdk5 was required for full virulence, probably because mutant cells are unable to sustain the dramatic polar growth required for the formation of the infective structures. These results support a major role for morphogenesis in the virulence program of dimorphic fungi.

Polarity proteins Bem1 and Cdc24 are components of the filamentous fungal NADPH oxidase complex

“…Attempts to isolate a deletion mutant of cdc24 in E. festucae were unsuccessful, presumably because Cdc24 is essential for growth as reported for cdc24 replacement mutants in S. cerevisiae, U. maydis and Ashbya gossypii (22,34,35). In contrast, the E. festucae ΔbemA mutant had relatively normal hyphal development with the exception of a slight loss in cell wall integrity, as detected by sensitivity to SDS, and swollen hyphal tips.…”

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

“…This gene encodes a cyclin that interacts specifically with Cdk5, an essential CDK with regulatory roles in morphogenesis in U. maydis (Castillo-Lluva et al, 2007). Cells defective in pcl12 showed drastic morphological changes that affect specifically to situations that demand a strong polar growth associated with the infection process, such as the formation of the b-dependent filament, the induction of the conjugation tubes, or the formation of a promycelium during spore germination.…”

“…In S. cerevisiae, Pcl cyclins specifically interact with the Pho85 kinase, whose ortholog in U. maydis is Cdk5 (Castillo-Lluva et al, 2007). To test physical interaction between the Cdk5 kinase and Pcl12 in U. maydis, we expressed an N-terminal VSV-tagged Pcl12 allele in a strain carrying a C-terminal myc-tagged functional cdk5 allele (Castillo-Lluva et al, 2007), and we performed a coimmunoprecipitation assay ( Figure 4B).…”

“…To test physical interaction between the Cdk5 kinase and Pcl12 in U. maydis, we expressed an N-terminal VSV-tagged Pcl12 allele in a strain carrying a C-terminal myc-tagged functional cdk5 allele (Castillo-Lluva et al, 2007), and we performed a coimmunoprecipitation assay ( Figure 4B). We found that VSVPcl12 associated with Cdk5-myc, supporting the notion of Pcl12 as a Pcl-like cyclin.…”

“…We found that VSVPcl12 associated with Cdk5-myc, supporting the notion of Pcl12 as a Pcl-like cyclin. To determine whether the interaction between Pcl12 and Cdk5 is specific (i.e., Pcl12 is not able to interact in U. maydis with other CDKs, such as the mitotic kinase Cdk1) , VSV-Pcl12 immunoprecipitates were also probed using anti-PSTAIRE antibodies that detect both Cdk5 and Cdk1 (Castillo-Lluva et al, 2007). No interaction was detected between Cdk1 and Pcl12 ( Figure 4C location of Pcl12, we fused a red fluorescent protein (RFP) tag to the C terminus of the endogenous pcl12 gene in AB33-derived cells carrying a cdk5-gfp allele.…”