A Putative Transcription Factor pcs1 Positively Regulates Both Conidiation and Sexual Reproduction in the Cereal Pathogen Fusarium graminearum

Abstract

The plant pathogen Fusarium graminearum causes Fusarium head blight in cereal crops and produces mycotoxins that are harmful to animals and humans. For the initiation and spread of disease, asexual and sexual reproduction is required. Therefore, studies on fungal reproduction contribute to the development of new methods to control and maintain the fungal population. Screening a previously generated transcription factor mutant collection, we identified one putative C2H2 zinc-finger transcription factor, pcs1, which is required for both sexual and asexual reproduction. Deleting pcs1 in F. graminearum resulted in a dramatic reduction in conidial production and a complete loss of sexual reproduction. The pathways and gene ontology of pcs1-dependent genes from microarray experiments showed that several G-protein related pathways, oxidase activity, ribosome biogenesis, and RNA binding and processing were highly enriched, suggesting that pcs1 is involved in several different biological processes. Further, overexpression of pcs1 increased conidial production and resulted in earlier maturation of ascospores compared to the wild-type strain. Additionally, the vegetative growth of the overexpression mutants was decreased in nutrient-rich conditions but was not different from the wild-type strain in nutrient-poor conditions. Overall, we discovered that the pcs1 transcription factor positively regulates both conidiation and sexual reproduction and confers nutrient condition-dependent vegetative growth.

Keywords: Conidiation; Fusarium graminearum; Gibberella zeae; sexual reproduction; transcription factor.

Fig. 1

Vegetative growth of G. zeae strains on CM and MM, and perithecia production on carrot agar. Z3639, wild-type strain; D-pcs1, pcs1 deletion mutant; O-pcs1, mutant with constitutive expression of pcs1. Photos were taken after a 5-d incubation on CM and MM, and 7 d after sexual induction on carrot agar.

Fig. 2

Asci and ascospores produced by outcrossing between the heterothallic strain Δmat1-1::hH1::GFP and D-pcs1. Photos were taken in an 8-day incubation after sexual induction. Only four out of eight mature ascospores in each ascus fluoresced as observed by a fluorescent microscopy with a GFP filter. Two images, differential interference contrast (left) and GFP fluorescence (center), were merged (right).

Fig. 3

Conidia production of F. graminearum strains on YMA. Black arrows indicate conidia produced from intercalary phialides on hyphae, and black arrowheads indicate conidia produced from intercalary phialides in false heads. White arrowheads indicate conidia produced from terminal phialides.

Fig. 4

Conidia germination after 0, 4, and 8 h incubation in minimal medium.

Fig. 5

Pathway enrichment of pcs1-dependent genes. Red and blue bars represent level of enrichment in positive and negative pcs1-dependent genes, respectively. We set a cut-off with a P value of < 0.05.

Fig. 6

Gene ontology (GO) enrichment of pcs1-dependent genes. (A) Cellular component, (B) biological process, (C) molecular function. Red and blue bars represent level of enrichment in positive and negative pcs1-dependent genes, respectively. We set a cut-off with a P value of < 0.05.