PLP 150C1 1st Edition Lecture 7Outline of Last Lecture I. Chestnut BlightII. Dutch Elm DiseaseIII. White Pine Blister RustIV. Other plant diseasesOutline of Current Lecture I. CharacteristicsII. King of yeastsIII. Sex lifeIV. Other important yeasts Current LectureYeasts are unicellular fungi.• Some can form short filaments of cells that don’t quite detach• Are evolved Ascomycetes• Reproduce by budding• Some normally filamentous ascomycetes and basidiomycetes have a yeast growth phase, often associated with life phase in which it is an internal pathogen of animals.Yeasts in our environment• Everywhere. Soil, on fruits, flowers & leaves, anywhere where there are sugar-containing substrates.• Many can be vectored by insects.• Can cope with a huge range of environmental conditions◦ Freezing temperatures, weird Ph’s, dry environments, high sugar concentrations, alcohol.Saccharomyces cerevisiae, the King of Yeasts• Main yeast used in wine production, because of its high sugar, high acid, and high ethanol tolerance• Alcohol is made by yeast under anaerobic (NO OXYGEN) or low-oxygen conditions.• They’re also the yeast used in baking because it makes carbon dioxide from sugar really quickly• Used to make commercially important proteins cause it can be genetically engineered, it’s regarded as safe, and fermentation technology is highly advanced.• Most important eukaryotic model system in science.• Can be studies by powerful genetics molecular biology techniques. Many crucial features have been discovered 1st in yeast.• Is used in research to find out features & mechanisms & to generate new biotechnological processes.• Is a model organism in modern medicine?• Used for drug screening & functional analysis of specific genes because it’s a eukaryote but isn’t complicated & can be handled as easily as bacteria.It’s a eukaryote• Norma eukaryotic structure with various organelles, just like us.• Unicellular organism with ability to make pseudohyphae.• Divides by budding while Schizosaccharomyces pombe divides by fission (called fission yeast)◦ Budding results in two cells of unequal size, a mother (old cell), and a daughter (new cell)• Yeast life isn’t indefinite; yeast cells age and mothers die after about 30-40 divisions.Yeast has a sex life!• Yeast cells can proliferate both as haploids and as diploids.• Haploid cells have one of two mating types, + or -. Not male & female.• Two haploid cells can mate to form a zygote; since yeast can’t move, cells must grow towards each other.• The diploid zygote starts dividing after mating.• Under nitrogen starvation diploid cells undergo meiosis & sporulation to form an ascus with four haploid spores.• Thus, although yeast is unicellular, we can distinguish different cell types with different genetic background.Other important yeasts• Fission yeast: elongates, cuts cell down the middle, you get two equal halves.• Beer/lager yeast: ferments sugar to alcohol.• Milk yeast: lactose fermentation to lactic acid.• Pichi or Yarrowia species: make methane from