A Large-Scale Functional Analysis of Putative Target Genes of Mating-Type Loci Provides Insight into the Regulation of Sexual Development of the Cereal Pathogen Fusarium graminearum

Abstract

Fusarium graminearum, the causal agent of Fusarium head blight in cereal crops, produces sexual progeny (ascospore) as an important overwintering and dissemination strategy for completing the disease cycle. This homothallic ascomycetous species does not require a partner for sexual mating; instead, it carries two opposite mating-type (MAT) loci in a single nucleus to control sexual development. To gain a comprehensive understanding of the regulation of sexual development in F. graminearum, we used in-depth and high-throughput analyses to examine the target genes controlled transcriptionally by two-linked MAT loci (MAT1-1, MAT1-2). We hybridized a genome-wide microarray with total RNAs from F. graminearum mutants that lacked each MAT locus individually or together, and overexpressed MAT1-2-1, as well as their wild-type progenitor, at an early stage of sexual development. A comparison of the gene expression levels revealed a total of 1,245 differentially expressed genes (DEGs) among all of the mutants examined. Among these, genes involved in metabolism, cell wall organization, cellular response to stimuli, cell adhesion, fertilization, development, chromatin silencing, and signal transduction, were significantly enriched. Protein binding microarray analysis revealed the presence of putative core DNA binding sequences (ATTAAT or ATTGTT) for the HMG (high mobility group)-box motif in the MAT1-2-1 protein. Targeted deletion of 106 DEGs revealed 25 genes that were specifically required for sexual development, most of which were regulated transcriptionally by both the MAT1-1 and MAT1-2 loci. Taken together with the expression patterns of key target genes, we propose a regulatory pathway for MAT-mediated sexual development, in which both MAT loci may be activated by several environmental cues via chromatin remodeling and/or signaling pathways, and then control the expression of at least 1,245 target genes during sexual development via regulatory cascades and/or networks involving several downstream transcription factors and a putative RNA interference pathway.

The FgSRP1 SR‐protein gene is important for plant infection and pre‐mRNA processing in Fusarium graminearum

“…In M. oryzae , PTH11 is important for appressorium formation and pathogenicity (DeZwaan et al ., ). Related to its defect in perithecium formation, the Fgsrp1 mutant was significantly reduced in the expression levels of the FgPPG1 pheromone precursor gene, FgICL1 , FGRRES_01763 and FGRRES_00404 that are known to be important for sexual reproduction in F. graminearum (Lee et al ., ; Kim et al ., ; Son et al ., ). A number of genes related to secondary metabolism, such as PKS12 , AURJ, ARUF , GIP1 and TRI101 also were reduced over twofold in the Fgsrp1 mutant (Supporting Information Table S1).…”

Large‐scale molecular genetic analysis in plant‐pathogenic fungi: a decade of genome‐wide functional analysis

“…Mutants of genes controlling sexual development formed barren perithecia, a smaller number of perithecia or no perithecia. Other mutants showed larger perithecia, delayed production of perithecia and perithecia with stage‐specific defects (Kim et al ., ). Mutants of genes controlling pleiotropic phenotypes represented 12 genes.…”

“…() constructed 127 knock‐out strains in F. graminearum strain Z3643 from 127 genes that were differentially expressed during sexual development (Table ). These genes were selected from 1245 genes based on their expression profiles and putative functional roles (Kim et al ., ). Forty genes in this collection control sexual and hyphal development, as well as virulence and a number of pleiotropic phenotypes.…”

Fungal Morphogenesis, from the Polarized Growth of Hyphae to Complex Reproduction and Infection Structures

“…While MAT loci from the Eurotiales usually carry a single TF-encoding gene, loci from the Sordariales usually have two or more genes for additional TFs. In the homothallic euascomycetes F. graminearum and S. macrospora, some, but not all, MAT locus-encoded TFs are required for the production of fertile perithecia (347,348). A protein binding microarray analysis with the F. graminearum HMG TF domain (MAT1-2-1) revealed 25 target genes that are specifically required for sexual development (347).…”

“…In the homothallic euascomycetes F. graminearum and S. macrospora, some, but not all, MAT locus-encoded TFs are required for the production of fertile perithecia (347,348). A protein binding microarray analysis with the F. graminearum HMG TF domain (MAT1-2-1) revealed 25 target genes that are specifically required for sexual development (347). A recent genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) analysis with the ␣1-box-containing TF (MAT1-1-1) from the heterothallic fungus Penicillium chrysogenum identified a DNA-binding motif that is highly conserved among euascomycetes and discovered several target genes directly involved in sexual development, such as ppg1, the homologue of the S. cerevisiae ␣-factor pheromone gene, and pre1, the ScSTE3 homologue (349).…”