The L-type calcium ion channel cch1 affects ascospore discharge and mycelial growth in the filamentous fungus Gibberella zeae (anamorph Fusarium graminearum).

Cch1, a putative voltage-gated calcium ion channel, was investigated for its role in ascus development in Gibberella zeae. Gene replacement mutants of CCH1 were generated and found to have asci which did not forcibly discharge spores, although morphologically ascus and ascospore development in the majority of asci appeared normal. Additionally, mycelial growth was significantly slower, and sexual development was slightly delayed in the mutant; mutant mycelia showed a distinctive fluffy morphology, and no cirrhi were produced. Wheat infected with Deltacch1 mutants developed symptoms comparable to wheat infected with the wild type; however, the mutants showed a reduced ability to protect the infected stalk from colonization by saprobic fungi. Transcriptional analysis of gene expression in mutants using the Affymetrix Fusarium microarray showed 2,449 genes with significant, twofold or greater, changes in transcript abundance across a developmental series. This work extends the role of CCH1 to forcible spore discharge in G. zeae and suggests that this channel has subtle effects on growth and development.

Gene family encoding the major toxins of lethal Amanita mushrooms.

Amatoxins, the lethal constituents of poisonous mushrooms in the genus Amanita, are bicyclic octapeptides. Two genes in A. bisporigera, AMA1 and PHA1, directly encode alpha-amanitin, an amatoxin, and the related bicyclic heptapeptide phallacidin, a phallotoxin, indicating that these compounds are synthesized on ribosomes and not by nonribosomal peptide synthetases. alpha-Amanitin and phallacidin are synthesized as proproteins of 35 and 34 amino acids, respectively, from which they are predicted to be cleaved by a prolyl oligopeptidase. AMA1 and PHA1 are present in other toxic species of Amanita section Phalloidae but are absent from nontoxic species in other sections. The genomes of A. bisporigera and A. phalloides contain multiple sequences related to AMA1 and PHA1. The predicted protein products of this family of genes are characterized by a hypervariable "toxin" region capable of encoding a wide variety of peptides of 7-10 amino acids flanked by conserved sequences. Our results suggest that these fungi have a broad capacity to synthesize cyclic peptides on ribosomes.

Gene expression shifts during perithecium development in Gibberella zeae (anamorph Fusarium graminearum), with particular emphasis on ion transport proteins.

Gibberella zeae, the causal agent of Fusarium head blight, is a devastating pathogen of small grains worldwide. The sexual cycle is a crucial component of head blight epidemiology, as forcibly discharged ascospores serve as the primary inoculum. The recent development of an Affymetrix GeneChip containing probesets representative of all predicted genes of G. zeae has opened the door to studies of differential gene expression during sexual development. Using GeneChips, a developmental time course was performed in culture, from vegetative hyphae to mature perithecia with multiseptate ascospores. Time-points represent the development of the major cell types comprising the mature perithecium. The majority of the 17,830 G. zeae probesets, 78%, were expressed during at least one of the developmental stages; 12% of these appear to be specific to sexual development. Analysis of the 162 predicted ion transporter genes is reported in detail, due to their association with perithecium function. Expression patterns of the MirA-type siderophores, chloride channels, P-type ATPases and potassium transporters show some specialization in regard to developmental stage. This is the first whole-genome analysis of differential transcript accumulation during sexual development in a filamentous fungus.

Taxonomy and toxicity of Conocybe lactea and related species.

Conocybe lactea was examined as part of a larger study on the distribution of amatoxins and phallotoxins in fungi, and the taxonomic relationships between these fungi. As amatoxins are present in the congener C. filaris, the locally abundant C. lactea was examined using HPLC and mass spectroscopy. Amatoxins were not found in C. lactea, but the related phallotoxins were present in small quantities making it the first fungus outside of the genus Amanita in which phallotoxins have been detected. Despite the presence of a related toxin, C. lactea was found not to be taxonomically close to C. filaris. Phylogenetic analyses using nuclear ribosomal RNA genes indicated that North American specimens of C. lactea were conspecific with North American specimens of C. crispa in Conocybe sect. Candidae. European C. crispa was a distinct taxon. The implications of the use of the name C. albipes for these taxa are discussed. Nucleotide data confirmed placement of the sequestrate taxon Gastrocybe lateritia in sect. Candidae, but as a distinct taxon. It is hypothesized that the unique sequestrate morphology of G. lateritia may be caused by a bacterial infection.