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Storage compounds – retaining nutrients

Storage compounds – retaining nutrients

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Storage compounds – retaining nutrients

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  1. lipid glycogen Littlefield and Heath 1979 Ultrastructure of Rust Fungi Storage compounds – retaining nutrients

  2. Nutrition of biotrophs • Components are extracted through haustoria • Nutrients are soluble and organic • Extracellular degradation for cell penetration • Extracellular factors establish/maintain a compatible infection • Suppress senescence

  3. Suppressing senescence www.mpiz-koeln.mpg.de/schlef/PSL_webpage.html

  4. Livning substrates exploited by fungi What is the nutrient flow direction? http://www.ucmp.berkeley.edu/fungi/rhyniefungus.jpg

  5. Arbuscular and ectomycorrhizal fungi

  6. Amino acid biosynthesis

  7. Secondary metabolites • Glucose-derived – polysaccharides, peptidopolysaccharides, and sugar alcohols. • Condensation products of acetate – derived from the acetate-malonate pathway of fatty acid synthesis, e.g. polyketides and phenolics. • Condensation products of acetate derived from the mevalonic acid pathway, e.g. terpenes. • Phenolics derived from the shikimic acid pathway of aromatic amino acid synthesis. • Derivatives of other amino acid syntheses.

  8. Secondary metabolites Pigments Hormones Toxins Co-regulated with sporulation

  9. Secondary metabolites of Saccharomyces www.crc.dk/flab/ newpage13.htm

  10. Genetics – study of heredity • Transmission - the passage of traits from one generation to the next

  11. Genetics – study of heredity • Population - genetic diversity and change within natural populations

  12. Genetics – study of heredity • Molecular - details of gene structure and function

  13. Our focus for genetics • transmission and molecular genetics in experimental systems • defining a population • organisms in culture • humungous fungus • vegetative incompatibility

  14. Transmission genetics • Typical characteristics of fungal genomes Small • S. cerevisiae 6 MB – 6000 genes • A. nidulans 13 MB – 12000 genes • H. sapiens 1300 MB – 30000 genes

  15. Typical characteristics of fungal genomes • Little repetitive DNA – single copy genes • 50-60% of nuclear genome is transcribed into mRNA in S cerevisiae • 33% in S. commune (basidiomycete) • 1% in humans • Introns • few, often none • small – 50-200bp vs ≥10 kb in mammals

  16. Most higher fungi are vegetative haploids • One genome copy per nucleus • Alternatives? • Plants? • Algae? • Animals?

  17. Risks of haploidy • No backup copy in case of genetic damage from UV or chemical mutagens • Yeasts tend to be diploid (S. cerevisiae except for lab strains) or have short G1 (S. pombe) Chant and Pringle JCB 129:751

  18. Advantages of haploidy • A multinucleate cell can expose genome to mutagens • most mutations are deleterious • select for advantageous mutations in a heterokaryotic system • Phenotypes of recessive mutations are obvious in the vegetative state, without generating homozygous recessives • Lab strains of S. cerevisiae now generally include a mutation which stabilizes the haploid state

  19. Transmission genetics – passage of inheritance • Similar to more familiar mammalian systems, with bulk of life cycle haploid • ‘Genders' are ‘mating types’ • cells are biochemically distinct but morphologically identical

  20. Fungal mating systems

  21. No mating factorsA. nidulans • Inbreeding possible • disadvantage – sex does not necessarily increase genetic diversity • advantage – can form resistant spores even if no mating partner is available • A. nidulans ascospores from 1995 still viable after 4°C storage, whereas conidia viability is severely reduced after several months at 4°C

  22. One factor (zygo, asco, some basids) • Bipolar mating system • meiosis will give two types of segregants • N. crassaa and  • Rhizopus+ and –

  23. One factor (zygo, asco, some basids) • Advantage – outbreeding • Disadvantage – cannot produce resistant sexual spores unless a partner is available • ‘Coping’ with one-factor mating systems • Some fungi have multiple alleles at the mating locus • Mating type switching in Saccharomyces

  24. One factor (zygo, asco, some basids) • In S. cerevisiae "a" cells produce a-factor, a peptide sexual hormone, and -receptor; converse for  cells • hormones/receptors interaction promotes schmooing, wall changes promote adhesion

  25. Two factors, A/B (often in basids) • Tetrapolar mating system  meiosis give four types of segregants • A1B1 :: A2B2A1B1, A1B2, A2B1, A2B2

  26. A and B functions are distinct • in homobasids (.....?) • A controls pairing and synchronous division of nuclei, hook cell formation; • B controls septal dissolution and hook cell fusion (b-glucanase activity) and nuclear migration

  27. A and B functions are distinct • in heterobasids (....?) • A controls pathogenicity; • B controls filamentous growth

  28. Systems restricting outcrossing in one-factor mating type systems • self-fertilityS. cerevisiae has "mating type switching" • molecular basis both mating genes have a storage site and an expression site. • if the appropriate partner cell is not available when mating conditions are presented (how would this be detected?)will induce swi expression

  29. Systems restricting outcrossing in one-factor mating type systems • vegetative (somatic) incompatibility • het genes are important for mating, but prevent vegetative fusion

  30. Systems restricting outcrossing in one-factor mating type systems • vegetative (somatic) incompatibility • in Fusarium – vegetative incompatibility is important for maintaining distinct populations with different host specificities • Fusarium oxysporum f. sp. groups

  31. Mutants in experimental fungal systems • spontaneous mutations or mutagenesis (uv, chemicals) • each gene is named for 1st described mutation • Example: gene for pigmentation is called “white” because the mutant lacked colouration

  32. Different species,different naming system • Saccharomyces cerevisiae • Schizosaccharomyces pombe • Aspergillus nidulans • Neurospora crassa • Generally, three-letters plus a letter or number – hypA, CDC2, cdc28