FoSTUA, Encoding a Basic Helix-Loop-Helix Protein, Differentially Regulates Development of Three Kinds of Asexual Spores, Macroconidia, Microconidia, and Chlamydospores, in the Fungal Plant PathogenFusarium oxysporum

Abstract

The soil-borne fungus Fusarium oxysporum causes vascular wilt of a wide variety of plant species. F. oxysporum produces three kinds of asexual spores, macroconidia, microconidia, and chlamydospores. Falcate macroconidia are formed generally from terminal phialides on conidiophores and rarely from intercalary phialides on hyphae. Ellipsoidal microconidia are formed from intercalary phialides on hyphae. Globose chlamydospores with thick walls are developed by the modification of hyphal and conidial cells. Here we describe FoSTUA of F. oxysporum, which differentially regulates the development of macroconidia, microconidia, and chlamydospores. FoSTUA encodes a basic helix-loop-helix protein with similarity to Aspergillus nidulans StuA, which has been identified as a transcriptional regulator controlling conidiation. Nuclear localization of FoStuA was verified by using strains expressing FoStuA-green fluorescent protein fusions. The FoSTUA-targeted mutants exhibited normal microconidium formation in cultures. However, the mutants lacked conidiophores and produced macroconidia at low frequencies only from intercalary phialides. Thus, FoSTUA appears to be necessary to induce conidiophore differentiation. In contrast, chlamydospore formation was dramatically promoted in the mutants. These data demonstrate that FoStuA is a positive regulator and a negative regulator for the development of macroconidia and chlamydospores, respectively, and is dispensable for microconidium formation in cultures. The disease-causing ability of F. oxysporum was not affected by mutations in FoSTUA. However, the mutants produced markedly fewer macroconidia and microconidia in infected plants than the wild type. These results suggest that FoSTUA also has an important role for microconidium formation specifically in infected plants.

<i>Bacillus subtilis Strains</i> with Antifungal Activity against the Phytopathogenic Fungi

“…Antifungal action of Bacillus metabolites may be due to disruption of fungal cell wall and inhibition of normal conidia development. It is known that chlamydospores with thick walls are developed by the modification of hyphal and conidial cells under unfavorable environmental conditions, such as at low temperature, and these resting bodies act as primary inocula in subsequent soil-borne infections, whereas the microconidia and macroconidia formed by F. oxysporum are important in secondary infection [35] [36]. Minerdi et al [37] reported that microbial symbionts silence the virulence of F. oxysporum and that changes in cell morphogenesis by F. oxysporum underlie this suppression.…”

The Transcription Factor StuA Regulates Central Carbon Metabolism, Mycotoxin Production, and Effector Gene Expression in the Wheat Pathogen Stagonospora nodorum

“…In studies of G. cingulata, the stuA deletion mutants failed to infect intact apple fruit due to failure to generate normal turgor pressure within the wild-type-appearing appressorium (33). However, in studies of A. fumigatus and F. oxysporum, the deletion mutant still caused disease (18,21).…”

“…Similarly, in Aspergillus fumigatus, Fusarium oxysporum, and Glomerella cingulata, deletion of the StuA ortholog resulted in mutants with reduced and abnormal conidiospore formation (18,21,33). In studies of G. cingulata, the stuA deletion mutants failed to infect intact apple fruit due to failure to generate normal turgor pressure within the wild-type-appearing appressorium (33).…”

“…Proteins with the conserved APSES (ASM-1, Phd1, StuA, EFG1, and Sok2) domain (1) belong to a class of transcription factors unique to the ascomycetes that regulate developmental differentiation (3,5,7,15,18,20,21,33,35). The APSES domain was modeled as a basic helix-loop-helix (bHLH)-like structure and binds to a specific stress response element (STRE) with the consensus sequence (A/T)CGCG(T/A)N(A/ C) (7).…”

Inoculum padronization for the production of cutinase by Fusarium oxysporum

“…Chlamydospores are the third type of spore and are either one or two celled. They are thick-walled spores filled with lipidlike material that serves to carry the fungus when a suitable host is not available, and can remain dormant in soil and infect other hosts for as long as 30 years (1,11,12).…”