The Ustilago maydis Cys₂His₂‐type zinc finger transcription factor Mzr1 regulates fungal gene expression during the biotrophic growth stage

Abstract

SummaryThe smut fungus Ustilago maydis establishes a biotrophic relationship with its host plant maize to progress through sexual development. Here, we report the identification and characterization of the Cys2His2-type zinc finger protein Mzr1 that functions as a transcriptional activator during host colonization. Expression of the U. maydis mig2 cluster genes is tightly linked to this phase. Upon conditional overexpression, Mzr1 confers induction of a subset of mig2 genes during vegetative growth and this requires the same promoter elements that confer inducible expression in planta. Furthermore, expression of the mig2-4 and mig2-5 genes during biotrophic growth is strongly reduced in cells deleted in mzr1. DNA-array analysis led to the identification of additional Mzr1-induced genes. Some of these genes show a mig2-like plantspecific expression pattern and Mzr1 is responsible for their high-level expression during pathogenesis. Mzr1 function requires the b-dependently regulated Cys 2His2-type cell cycle regulator Biz1, indicating that two stage-specific regulators mediate gene expression during host colonization. In spite of a role as transcriptional activator during biotrophic growth, mzr1 is not essential for pathogenesis; however, conditional overexpression interfered with proliferation during vegetative growth and mating ability, caused a cell separation defect, and triggered filamentous growth. We discuss the implications of these findings.

The Biotrophic Development of Ustilago maydis Studied by RNA-Seq Analysis

“…They all have a reasonably strong connectivity to the magenta module of > 0.9 ( Figure 7C). Consistently, mzr1 has been demonstrated to be involved in the expression of several effector genes (Zheng et al, 2008), which we now place in the magenta module (Supplemental Data Sets 12). However, in contrast to hdp2 and biz1 (Flor-Parra et al, 2006;Heimel et al, 2010b;Lanver et al, 2014), mzr1 is not a major virulence factor (Zheng et al, 2008), most likely because biz1 and hdp2 can compensate for the lack of mzr1 during infection.…”

“…Those transcription factors have previously been suggested to be the main inducers of early effectors (Heimel et al, 2010b;Lanver et al, 2014). Furthermore, our analysis suggests UMAG_11658, UMAG_00501, mzr1 (mig2-5 zinc finger regulator1, UMAG_05804) (Zheng et al, 2008) and UMAG_02104 ( Figure 7C) as being involved in early effector gene expression. They all have a reasonably strong connectivity to the magenta module of > 0.9 ( Figure 7C).…”

“…All these studies were performed with the engineered solopathogenic haploid strain SG200 (Kamper et al, 2006) that can infect plants without a mating partner. The transcriptome of the U. maydis SG200 strain as well as of SG200 mutants during pathogenic development has been investigated in several studies using array technology (Kamper et al, 2006;Zheng et al, 2008;Skibbe et al, 2010;Gao et al, 2013;Schuler et al, 2015;Rabe et al, 2016). A few studies also analyzed the transcriptome of compatible wild-type strains at discrete stages after infection (Wahl et al, 2010;Zahiri et al, 2010;Tollot et al, 2016).…”

The Mitochondrial Dnm1-Like Fission Component Is Required for lga2 -Induced Mitophagy but Dispensable for Starvation-Induced Mitophagy in Ustilago maydis

“…Gene specific primers were the following: 5=-C GGTCAAACACGAAACCCTTTCTC-3=/5=-AGCTCCAGTACCAAACT CGTAGAC-3= (nad3), 5=-CACTCGGTGCTGTTCTTTCTGG-3=/5=-CA GGAAAAGTACTGTTACTGCTCC-3= (nad6), 5=-GCTCCTGATATGG CATTCCCTCG-3=/5=-CCTGTTCCTGCCCCTTGTTCTAC-3= (cox1), 5=-TCCGGTTCATCGTAACTGGTGC-3=/5=-ACTCCTTCACGCTCGA TAAGAACG-3= (cox2). Results were normalized against the expression of the probable TATA box binding factor gene tbp (um10143) as described previously (44).…”

The Effectors of Smut Fungi

“…In the promoter of mig2-5, a cis-active element conferring a strong transcriptional activation during biotrophic growth was mapped (Farfsing et al, 2005) and Mzr1, a zinc finger transcription factor upregulated during plant colonization, was shown to control in planta expression of the mig2-5 gene (Zheng et al, 2008). There appears to be an interplay connection between expression of the b-regulated biz1 transcription factor (Flor-Parra et al, 2006) and mrz1, but whether this occurs on a transcriptional level or posttranscriptionally remains to be sorted out (Zheng et al, 2008). Microarray analyses identified 50 Mzr1-induced U. maydis genes of which many encode secreted proteins.…”