A Class-V Myosin Required for Mating, Hyphal Growth, and Pathogenicity in the Dimorphic Plant PathogenUstilago maydis [W]

Abstract

In the early stages of plant infection, yeast-like haploid sporidia of Ustilago maydis respond to pheromone secreted by compatible partners by forming conjugation tubes. These then fuse to generate a dikaryotic hypha that forms appressoria to penetrate the host plant. As a first step toward understanding the structural requirements for these transitions, we have identified myo5 , which encodes a class-V myosin. Analysis of conditional and null mutants revealed that Myo5 plays nonessential roles in cytokinesis and morphogenesis in sporidia and is required for hyphal morphology. Consistent with a role in morphogenesis, a functional green fluorescent protein-Myo5 fusion protein localized to the bud tip and the hyphal apex as well as to the septa and the spore wall during later stages of infection. However, the loss of Myo5 did not affect the tip growth of hyphae and sporidia. By contrast, Myo5 was indispensable for conjugation tube formation. Furthermore, myo5 mutants were impaired in the perception of pheromones, which indicates a particular importance of Myo5 in the mating process. Consequently, few mutant hyphae were formed that penetrated the plant epidermis but did not continue invasive growth. These results indicate a crucial role of Myo5 in the morphogenesis, dimorphic switch, and pathogenicity of U. maydis .

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

“…In agreement with some role of Pcl12 in the formation of the conjugation tubes, we found that pcl12 was induced after pheromone treatment ( Figure 7C). These data suggest that Pcl12 plays a role in the polar growth of the conjugation tube, although we cannot exclude some indirect effect such as the possibility that Pcl12 participate in pheromone sensing as it has been recently proposed for Myo5 and Yup1 (Weber et al, 2003;Fuchs et al, 2006). To address this issue, we took advantage of the fuz7DD allele, which encodes an activated version of the mitogenactivated protein kinase (MAPK) kinase involved in pheromone response (Banuett and Herskowitz, 1994;Mü ller et al, 2003), since cells expressing this allele under the arabinose-induced crg1 (D) Pcl12-induced filamentation is dependent on cdk5.…”

“…To distinguish between these possibilities, we introduced a fusion protein of GFP and Myo5, a class V myosin from U. maydis that is transported via actin cables toward the growing end of the cell (Weber et al, 2003). GFP-Myo5 signal appeared at the filament tip in control and mutant cells ( Figure 3C), indicating that the ability to detect and direct transport toward the hyphal tip was not impaired.…”

“…Plasmids for GFP tagging of fimbrin, myosin V, and a-tubulin were already described (Steinberg et al, 2001;Weber et al, 2003;CastilloLluva et al, 2007). Plasmids allowing the constitutive expression of cfp and yfp genes were described by Flor-Parra et al (2006).…”

The RNA-binding protein Rrm4 is essential for polarity inUstilago maydisand shuttles along microtubules

“…Potential proteins that need to be localised by mRNA transport in U. maydis include enzymes involved in cell wall synthesis, such as chitin synthases (Weber et al, 2003), components of the endocytosis machinery (Steinberg et al, 2001), regulatory proteins such as small G proteins (Mahlert et al, 2006), or cell-shape determinants such as septins (Boyce et al, 2005). The latter example is of particular interest, because septins were initially identified to function during septation in S. cerevisiae (Gladfelter, 2006) and localise at the hyphal tip as well as the distal septum in filaments of Candida albicans (Warenda and Konopka, 2002).…”

The Ustilago maydis a2 Mating-Type Locus Genes lga2 and rga2 Compromise Pathogenicity in the Absence of the Mitochondrial p32 Family Protein Mrb1

“…For construction of pRIYC1, genomic FB2 DNA was amplified with primers RG1/RG2 (59-CATGCCATGGAAAA-GATTCGCCCCACATTG-39/59-GAGCTCATGAAACGCTTTCGTCTCCA-CCTTC-39). PCR products were digested with NcoI/BspHI and inserted into the NcoI site of plasmid p123-YFP, which enables YFP expression under the otef promoter (Weber et al, 2003). For construction of pRAGC1, genomic FB2 DNA was amplified with primers RG1/RG3 (59-GAGCTCATGAGACGAGGTGCGTCAGC-39).…”