Fungal growth and development

• isometric growth

  growth that occurs at the same rate for all parts of an organism so that its shape is consistent throughout development
• polarised growth

  requires that the flow of secretory vesicles is directed towards a single site on the cell cortex
• what is hypha

  basic unit of growth, can be septate or coenocytic, contains microtubules, connecting compartments allowing intercellular communication and reallocation of resources
• characteristics of hyphal tips

  • polarised
  • change direction
  • show autotrophism
• functions of fungal cell wall

  • maintenance of cell shape - determines the morphology of the hypha or other fungal cells
  • stabilisation of the internal osmotic conditions - wall is sturdy and creates a counteracting pressure which stops excessive water influx
  • protection against physical stress - combination of mechanical strength and high elasticity allows the wall to redistribute physical stresses
  • scaffold for extracellular proteins and secreted enzymes - glycoproteins on scaffold limit the permeability of the wall
• what do septa do

  • permit regulated flow of material 
  • either complete (imperforate) or regulated (perforate)
  • permit compartmentalisation of cells and hence differentiation
• what is a woronin body

  a proteinaceous body contained by perforate in ascomycota
• what are dolipores

  septa in Basidomycota are protected by a cap known as the parenthosome
• what factors drive hyphal extension

  • turgor pressure - closed hydraulic system
  • steady-state or balanced lysis using the vesicle supply centre or spitzenkorper
• duplication cycle in fungi

  an important point of contrast between the duplication cycle of fungi and those of animals and plants is that in fungi there is no necessary quantitative or spatial relationship between division of the nuclei and division of the cytoplasm by cross-wall formation (septation)
• hyphae steering mechanism

  • thigmotropic response - touch stimulus
  • chemotropic response - chemical stimulus
  • autotropic response - light stimulus
  • galvanotropic repsonse - response to an electric current
• in what ways can hyphae anastomose to form a complex interconnected network

  • tip to tip
  • tip to side
  • self fusions and non self fusions
  • specialised fusions e.g. clamp connections
  • conidial anastomosis tubes CATs - formation of mycelial network
• ways mycelia forage for resources

  • non-resource unit restricted fungi
  • explore
  • capture
  • exploit
  • consolidate
  • combat
  • disseminate - spread
• mycelia exhibit phases of growth

  • if the growth of the culture is followed by measuring biomass such a growth pattern can be shown to occur in the conventional sequence of phases of growth of a culture of a unicellular microorganism
  • lag, exponential, linear, deceleration
• mycelia are often resource unit restricted

  • maturing mycelia become affected by nutrient limitation, change in pH and growth inhibitors (metabolic waste products and secondary metabolites that the mycelium produces)
  • essentially fungi show heterogenous growth patterns under resourse unit restricted conditions
• where are colonies growing in terms of physiological age

  the youngest actively extending hyphae at the edge of the fungal colony and the oldest, non-extending, sporulating mycelium at the centre 
• generative hyphae

  hyphae that bear clamp connections or spores
• skeletal hyphae

  long unbranched, thin or thick walled hyphae
• binding hyphae

  thick walled hyphae that branch frequently 
• monomotic hyphal system

  a fruitbody with only generative hyphae
• dimitic and trimitic hyphal systems

  fruitbodies with two or more types of hyphae
• which hyphae are usually empty of cell contents

  • skeletal and binding
  • it is these empty hyphae that make many polypores so tough and hard
• sclerotia


  for survival
• mycelial cords

  foraging
• rhizomorphs

  foraging and translocation
• conidiation

  production of asexual spores
• what does mating in zygomycota require

  cooperative metabolism between + and - mating types
• process of mating in zygomycota

  1. Mycelia form. If the two mating types (+ and -) are in close proximity, extensions called gametangia form between them.
  2. Fusion between + and - mating types results in a zygosporangium with multiple haploid nuclei. The zygosporangium forms a thick, protective coat.
  3. The nuclei tuse to form a zygote with multiple diploid nuclei.
  4. A sporangium grows on a short stalk. Haploid spores are formed inside
• sexual spores in ascomycota

  typical ascus contains eight ascospores
• mating process of S. cerevisiae (ascomycota)

  • controlled by a complex genetic locus called MAT at which two linked genes are located
  • MATa locus encodes a1 and a2 polypeptides, the messengers for which are transcribed in opposite directions
  • MATalpha encodes polypeptides alpha1 and alpha2
• what facilitates mating type switching in ascomycota

  cassete based gene conversion
• homophallic

  self fertile
• heterophallic

  sex requires a partner
• monokaryon

  uninucleate haploid
• homokaryon

  uni or multi nucleate haploid
• dikaryon

  binucleate haploid
• heterokaryon

  multinucleate
• bifactorial tetrapolar breeding system

  mating type is determined by two unlinked loci; compatibility at both loci is required for mating to occur.
• what maintains dikaryons

  clamp connections, ensures every hyphal compartment within a mycelium is binucleate
• somatogamous mating

  male and female nuclei are brought together by fusion of vegetative hyphae originating from mycelia of opposite mating types.