Noble-rotted grapes are colonized by complex microbial populations. I isolated pigment-producing Metschnikowia strains from noble-rotted grapes that had antagonistic activity against filamentous fungi, yeasts, and bacteria. A red-maroon pigment was formed from a diffusible colorless precursor released by the cells into the medium. The conversion of the precursor required iron and could occur both in the cells (red colonies) and in the medium (red halos around colonies). The intensity of pigmentation was correlated with the intensity of the antimicrobial activity. Mutants that did not form pigment also lacked antifungal activity. Within the pigmented halos, conidia of the sensitive fungi did not germinate, and their hyphae did not grow and frequently lysed at the tips. Supplementation of the medium with iron reduced the size of the halos and the inhibition zones, while it increased the pigment accumulation by the colonies. The iron-binding agent tropolone had a similar effect, so I hypothesize that pigmented Metschnikowia isolates inhibit the growth of the sensitive microorganisms by pigment formation, which depletes the free iron in the medium. As the pigment is a large nondiffusible complex produced in the presence of both low and high concentrations of ferric ions, the proposed mechanism is different from the mechanisms operating in microbes that release siderophores into the environment for iron acquisition.The important problems for postharvest protection of fruit include the declining effectiveness of registered fungicides, public pressure to reduce fungicide use, and public demand for produce free of synthetic pesticides. One solution is to use microorganisms with antifungal effects as biocontrol agents to reduce or inhibit the rate of propagation of destructive fungi during storage. Antagonistic yeasts have received particular attention, as their activity usually does not depend on the production of antibiotics or other toxic secondary metabolites. For example, strains of Candida, Cryptococcus, Debaromyces, Metschnikowia, Pichia, Rhodotorula, Sporobolomyces, and Trichosporon all have been reported to inhibit postharvest decay of fruit due to their antifungal effects (6,18,36,38,40,44,50,52). The modes of action proposed for the inhibition process include competition for space and nutrients, parasitism, direct interaction with the pathogen, production of cell wall lytic enzymes, and induced resistance in the host tissue (for a review, see reference 47).Fruit-borne strains of Metschnikowia pulcherrima can be effective in protecting apples, peaches, and grapes against postharvest rot caused by Botrytis cinerea and other postharvest pathogens (14,36,48). The related species Metschnikowia fructicola is an effective biocontrol agent for postharvest diseases of grapes (25). M. pulcherrima, but not M. fructicola, produces a red pigment, pulcherrimin, that accumulates in the cells and in the medium near a colony (26,27). Pulcherrimin is a large complex formed nonenzymatically from a dibasic acid, pulcherriminic ac...

Schizosaccharomyces pombe cells divide by medial fission throughout contraction of an actomyosin ring and deposition of a multilayered division septum that must be cleaved to release the two daughter cells. Although many studies have focused on the actomoysin ring and septum assembly,little information is available concerning the mechanism of cell separation. Here we describe the characterization of eng1+, a new gene that encodes a protein with detectable endo-β-1,3-glucanase activity and whose deletion is not lethal to the cells but does interfere in their separation. Electron microscopic observation of mutant cells indicated that this defect is mainly due to the failure of the cells to degrade the primary septum, a structure rich in β-1,3-glucans, that separates the two sisters cells. Expression of eng1+ varies during the cell cycle,maximum expression being observed before septation, and the protein localizes to a ring-like structure that surrounds the septum region during cell separation. This suggests that it could also be involved in the cleavage of the cylinder of the cell wall that covers the division septum. The expression of eng1+ during vegetative growth is regulated by a C2H2 zinc-finger protein (encoded by the SPAC6G10.12c ORF), which shows significant sequence similarity to the Saccharomyces cerevisiae ScAce2p,especially in the zinc-finger region. Mutants lacking this transcriptional regulator (which we have named ace2+) show a severe cell separation defect, hyphal growth being observed. Thus, ace2p may regulate the expression of the eng1+ gene together with that of other genes whose products are also involved in cell separation.

β(1,3)glucan is critical for contractile ring positioning and for coupling septum synthesis to constriction of the contractile ring and plasma membrane extension during cytokinesis.

No abstract

Convergent evolution is common throughout the tree of life, but the molecular mechanisms causing similar phenotypes to appear repeatedly are obscure. Yeasts have arisen in multiple fungal clades, but the genetic causes and consequences of their evolutionary origins are unknown. Here we show that the potential to develop yeast forms arose early in fungal evolution and became dominant independently in multiple clades, most likely via parallel diversification of Zn-cluster transcription factors, a fungal-specific family involved in regulating yeast-filamentous switches. Our results imply that convergent evolution can happen by the repeated deployment of a conserved genetic toolkit for the same function in distinct clades via regulatory evolution. We suggest that this mechanism might be a common source of evolutionary convergence even at large time scales.

The ascomycetous yeasts traditionally referred to as the Saccharomyces sensu stricto complex are a group of closely related species that are isolated by a postzygotic barrier. They can easily hybridize; and their allodiploid hybrids propagate by mitotic divisions as efficiently as the parental strains, but can barely divide by meiosis, and thus rarely produce viable spores (sterile interspecies hybrids). The postzygotic isolation is not effective in allotetraploids that are able to carry out meiosis and produce viable spores (fertile interspecies hybrids). By application of molecular identification methods, double (Saccharomyces cerevisiae x Saccharomyces uvarum and S. cerevisiae x Saccharomyces kudriavzevii) and triple (S. cerevisiae x S. uvarum x S. kudriavzevii) hybrids were recently identified in yeast populations of fermenting grape must and cider in geographically distinct regions. The genetic analysis of these isolates and laboratory-bred hybrids revealed great variability of hybrid genome structures and demonstrated that the alloploid genome of the zygote can undergo drastic changes during mitotic and meiotic divisions of the hybrid cells. This genome-stabilization process involves loss of chromosomes and genes and recombination between the partner genomes. This article briefly reviews the results of the analysis of interspecies hybrids, proposes a model for the mechanism of genome stabilization and highlights the potential of interspecies hybridization in winemaking.

Schizosaccharomyces pombe cells divide by medial fission through contraction of an actomyosin ring and deposition of a multilayered division septum that must be cleaved to release the two daughter cells. Here we describe the identification of seven genes (adg1؉ , and mid2 ؉ ) whose expression is induced by the transcription factor Ace2p. The expression of all of these genes varied during the cell cycle, maximum transcription being observed during septation. At least three of these proteins (Eng1p, Agn1p, and Cfh4p) localize to a ring-like structure that surrounds the septum region during cell separation. Deletion of the previously uncharacterized genes was not lethal to the cells, but produced defects or delays in cell separation to different extents. Electron microscopic observation of mutant cells indicated that the most severe defect is found in eng1⌬ agn1⌬ cells, lacking the Eng1p endo-␤-1,3-glucanase and the Agn1p endo-␣-glucanase. The phenotype of this mutant closely resembled that of ace2⌬ mutants, forming branched chains of cells. This suggests that these two proteins are the main activities required for cell separation to be completed.

In the conserved 5?8S gene of the ITS1-5?8S-ITS2 region the difference is 8 %. The D1/D2 domain differs only at two nucleotides from the homologous sequence of a yeast strain isolated from botrytized grapes in California, suggesting that C. zemplinina is a wine yeast that occurs in geographically distant localities.