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

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

Suppressing senescence

Livning substrates exploited by fungi What is the nutrient flow direction?

Arbuscular and ectomycorrhizal fungi

Amino acid biosynthesis

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.

Secondary metabolites Pigments Hormones Toxins Co-regulated with sporulation

Secondary metabolites of Saccharomyces newpage13.htm

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

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

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

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

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

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 – bp vs ≥10 kb in mammals

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

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

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

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

Fungal mating systems

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

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

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

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

Two factors, A/B (often in basids) Tetrapolar mating system  meiosis give four types of segregants A 1 B 1 :: A 2 B 2  A 1 B 1, A 1 B 2, A 2 B 1, A 2 B 2

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 (  -glucanase activity) and nuclear migration

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

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

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

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

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

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