Saccharomyces cerevisiae centromere CEN11 does not induce chromosome instability when integrated into the Aspergillus nidulans genome

The Gibberellin Producer Fusarium fujikuroi: Methods and Technologies in the Current Toolkit

In recent years, there has been a noticeable increase in research interests on the Fusarium species, which includes prevalent plant pathogens and human pathogens, common microbial food contaminants and industrial microbes. Taken the advantage of gibberellin synthesis, Fusarium fujikuroi succeed in being a prevalent plant pathogen. At the meanwhile, F. fujikuroi was utilized for industrial production of gibberellins, a group of extensively applied phytohormone. F. fujikuroi has been known for its outstanding performance in gibberellin production for almost 100 years. Research activities relate to this species has lasted for a very long period. The slow development in biological investigation of F. fujikuroi is largely due to the lack of efficient research technologies and molecular tools. During the past decade, technologies to analyze the molecular basis of host-pathogen interactions and metabolic regulations have been developed rapidly, especially on the aspects of genetic manipulation. At the meanwhile, the industrial fermentation technologies kept sustained development. In this article, we reviewed the currently available research tools/methods for F. fujikuroi research, focusing on the topics about genetic engineering and gibberellin production.

The Thom Award address. Industrial mycology and the new genetics

The genetic investigation of fungi has been extended substantially by DNA-mediated transformation, providing a supplement to more conventional genetic approaches based upon sexual and parasexual processes. Initial transformation studies with the yeast Saccharomyces cerevisiae provided the model for transformation systems in other fungi with regard to methodology, vector construction and selection strategies. There are, however, certain differences between S. cerevisiae and filamentous fungi with regard to type of genomic insertion and the availability of shuttle vectors. Single-site linked insertions are common in yeast due to the high level of homology required for recombination between vectored and genomic sequences, whereas mycelial fungi often show a high frequency of heterologous and unlinked insertions, often in the form of random and multiple-site integrations. While extrachromosomally-maintained or replicative vectors are readily available for use with yeasts, such vectors have been difficult to construct for use with filamentous fungi. The development of vectors for replicative transformation with these fungi awaits further study. It is proposed that replicative vectors may be inherently less efficient for use with mycelial fungi relative to yeasts, since the mycelium, as an extended and semicontinuous network of cells, may delimit an adequate diffusion of the vector carrying the selectable gene, thus leading to a high frequency of abortive or unstable transformants.

Disruption of a Magnaporthe grisea cutinase gene

Using a one-step strategy to disrupt CUT1, a gene for cutinase, cut1- mutants were generated in two strains of Magnaporthe grisea. One strain, pathogenic on weeping lovegrass and barley and containing the arg3-12 mutation, was transformed with a disruption vector in which the Aspergillus nidulans ArgB+ gene was inserted into CUT1. Prototrophic transformants were screened by Southern hybridization, and 3 of 53 tested contained a disrupted CUT1 gene (cut1::ArgB+). A second strain, pathogenic on rice, was transformed with a disruption vector in which a gene for hyg B resistance was inserted into CUT1. Two of the 57 transformants screened by Southern hybridization contained a disrupted CUT1 gene (cut1::Hyg). CUT1 mRNA was not detectable in transformants that contained a disrupted gene. Transformants with a disrupted CUT1 gene failed to produce a cutin-inducible esterase that is normally detected by activity staining on non-denaturing polyacrylamide gels. Enzyme activity, measured either with tritiated cutin or with p-nitrophenyl butyrate as a substrate, was reduced but not eliminated in strains with a disrupted CUT1 gene. The infection efficiency of the cut1- disruption transformants was equal to that of the parent strains on all three host plants. Lesions produced by these mutants had an appearance and a sporulation rate similar to those produced by the parent strains. We conclude that the M. grisea CUT1 gene is not required for pathogenicity.

Centromeric DNA of Kluyveromyces lactis

A direct selection method was used to isolate centromeres from a genomic library of the yeast Kluyveromyces lactis. The method is based on the lethality at high copy number of the ochre-suppressing tRNA gene SUP11. Five different chromosomal fragments were found that confer mitotic stability to plasmids containing a replication origin of K. lactis (KARS). In addition, KARS plasmids containing these fragments have a copy number of approximately one, and each of the five fragments hybridizes to a different chromosome of K. lactis. From these results we conclude that five of the six centromeres of K. lactis have been isolated. These centromeres do not function in S. cerevisiae.

Yeast centromeres

Significant progress has been made toward understanding the roles played by conserved centromere DNA sequences in both mitotic and meiotic chromosome segregation. We are just beginning to formulate a picture of what a yeast kinetochore actually looks like and what components other than CEN DNA are necessary for function. In the next few years some of the genes encoding structural components of the kinetochore, and perhaps some involved in regulation of kinetochore function, will be cloned. Work is already in progress to isolate and characterize the proteins necessary for the assembly, maintenance and function of this amazing biological structure.