Fusarium graminearum is an important pathogen of small grains and maize in many areas of the world. To better understand the molecular mechanisms of F. graminearum pathogenesis, we used the restriction enzyme-mediated integration (REMI) approach to generate random insertional mutants. Eleven pathogenicity mutants were identified by screening 6,500 hygromycin-resistant transformants. Genetic analyses indicated that the defects in plant infection were tagged by the transforming vector in six of these mutants. In mutant M8, the transforming plasmid was integrated 110-bp upstream from the start codon of the cystathionine betalyase gene (CBL1). Gene replacement mutants deleted for CBL1 and the methionine synthase gene MSY1 were also obtained. Both the cbl1 and msy1 deletion mutants were methionine auxotrophic and significantly reduced in virulence on corn silks and wheat heads. We also identified genes disrupted by the transforming DNA in three other REMI mutants exhibiting reduced virulence. In mutants M68, the transforming vectors were inserted in the NADH: ubiquinone oxidoreductase. The putative b-ZIP transcription factor gene and the transducin beta-subunit-like gene disrupted in mutants M7 and M75, respectively, had no known homologs in filamentous fungi and were likely to be novel fungal virulence factors.
Fusarium head blight caused by Fusarium graminearum is an important disease of wheat and barley. In a previous study, we identified several mutants with reduced virulence by insertional mutagenesis. A transducin beta-like gene named FTL1 was disrupted in one of these nonpathogenic mutants. FTL1 is homologous to Saccharomyces cerevisiae SIF2, which is a component of the Set3 complex involved in late stages of ascospore formation. The ⌬ftl1 mutant was significantly reduced in conidiation and failed to cause typical disease symptoms. It failed to colonize the vascular tissues of rachis or cause necrosis on the rachis of inoculated wheat heads. The ⌬ftl1 mutant also was defective in spreading from infected anthers to ovaries and more sensitive than the wild type to plant defensins MsDef1 and osmotin. However, the activation of two mitogen-activated protein kinases, Mgv1 and Gpmk1, production of deoxynivalenol, and expression of genes known to be important for plant infection in F. graminearum were not affected, indicating that the defect of the ⌬ftl1 mutant in plant infection is unrelated to known virulence factors in this pathogen and may involve novel mechanisms. The ⌬ftl1 deletion mutant was significantly reduced in histone deacetylation, and many members of the yeast Set3 complex are conserved in F. graminearum. FTL1 appears to be a component of this well-conserved protein complex that plays a critical role in the penetration and colonization of wheat tissues.
The presence of unpaired copies of a gene during meiosis triggers silencing of all copies of the gene in the diploid ascus cell of Neurospora. This phenomenon is called meiotic silencing and on the basis of genetic studies appears to be a post-transcriptional gene silencing (PTGS) mechanism. Previously, meiotic silencing was defined to be induced by the presence of a DNA region lacking an identical segment in the homologous chromosome. However, the determinants of unpaired DNA remained a mystery. Using the Ascospore maturation-1 (Asm-1) gene, we defined what needs to be "unpaired" to silence a gene. For efficient silencing, an unpaired region of DNA needs to be of a sufficient size and contain homology to the reporter transcript. The greater the size of the loop and the larger the homology to the reporter transcript, the better the resulting meiotic silencing is. Conversely, regions not containing homology to the transcript, e.g., intergenic regions, did not silence the reporter. Surprisingly, unpaired fragments lacking a canonical promoter silenced the reporter. Additionally, we detected the unpairing-dependent loss of a transcript during meiotic silencing. Our observations further support a PTGS mechanism for meiotic silencing and offer insight into the evolutionary consequences resulting from this novel meiotic checkpoint.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.