Unknown,Transcriptomics,Genomics,Proteomics

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Ustilago maydis rak1 mediated gene expression during exponential growth

ABSTRACT: In mammalian cells RACK1 serves as a scaffold protein that has a role in integrating inputs from different signaling pathways and affects translation through association with ribosomes. U. maydis contains a seven-WD40 repeat motif protein designated Rak1, which shows 68% identity to RACK1 and is homologous to Asc1p of Saccharomyces cerevisiae. The asc1 mutant could be complemented by introduction of U. maydis rak1. The deletion of rak1 affected cell growth, cell wall integrity and specifically attenuated cell fusion. This latter defect was caused by reduced expression of prf1 encoding the regulator for pheromone and pheromone-receptor genes. Rak1 interacts with a variety of ribosomal proteins and microarray analysis revealed that the deletion of rak1 led to severely reduced expression of rop1, an activator prf1. The constitutive expression of rop1 could rescue the defect of mfa1 expression as well as conjugation tube formation in response to pheromone induction in the rak1 mutant. Moreover, a solopathogenic rak1 mutant failed to respond to plant derived stimuli, resulting in attenuated filamentation and pathogenicity. This could be partially rescued by constitutive expression of the b heterodimer. These data suggest that rak1 is a regulator of rop1 expression with additional roles after cell fusion. Ustilago maydis strains FB1 and FB1?rak1 were grown on a rotary shaker (200 rpm) in liquid Ustilago complete medium with 1% glucose at 28°C to an OD600 of 0.5. The experiment was performed using three independent biological replicates per strain.

ORGANISM(S): Ustilago maydis

SUBMITTER: Regine Kahmann

PROVIDER: E-GEOD-30382 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:In fungi, sexual compatibility is controlled by mating type loci that prevent self-fertilization. In the plant pathogenic fungus Ustilago maydis, the b mating type locus encodes a pair of unrelated homeodomain proteins, termed bE and bW. After fusion of two compatible, haploid cells, the bE and bW proteins form a heterodimeric complex, but only if they are derived from different, compatible alleles. The active bE/bW complex is required and sufficient to initiate pathogenic development of U. maydis, which is prerequisite for sexual reproduction of the fungus. However, the role of the b heterodimer during later stages of pathogenic development was unclear. To analyze b function during in planta development, we generated a temperature-sensitive bE allele (bEts) encoding a protein with a single amino acid alteration at the border of the homeodomain. This mutation leads to a stop in pathogenic development at the restrictive temperature in planta, while bEts strains show normal development at permissive temperature. At restrictive temperature, hyphae develop enlarged, bulbous cells at their tips that contain multiple nuclei, indicating a severe defect in cell division. DNA array analysis of bEts mutant strains in planta revealed a b-dependent regulation of genes coding for secreted proteins that were shown to influence fungal virulence. Our data demonstrate that in U. maydis the b heterodimer is not only essential to establish the heterodikaryon after mating of two compatible sporidia and to initiate fungal pathogenicity, but also to sustain in planta proliferation and ensure sexual reproduction. Maize plants were infected with a mixture of either FB1 and FB2 (wild-type), or RAb1ts and RAb2ts (temperature-sensitive b heterodimer) and kept at 22Â°C (permissive conditions). Control samples of FB1/FB2 and RAb1ts and RAb2ts were taken 5 days post inoculation at 22 Â°C (1 replicate each), to see if strains expressing the bts heterodimer show wildtype-like biotrophic development. To measure the impact of the b heterodimer on pathogenic development, infected plants were shifted for 9 hours to resrictive conditions (31Â°C) 111 hours post infection. After the temperature shift FB1/FB2 (3 replicates) infections developed normal, whereas RAb1ts/RAb2ts (3 replicates) infections were not able to further proliferate in planta because of a none-functional b heterodimer.

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Ustilago maydis rak1 mediated gene expression during exponential growth

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