Fungal Osmotrophy

Question 1

What does synapomorphy mean?

Answer 1

a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants.

Question 2

What are some candidates for synapomorphy?

Answer 2

Hyphal growth
Lack of flagella
Cell wall polymers and their genes
Lysine biosynthetic pathway
Osmotrophy

Question 3

Why can’t hyphal growth be used as a synapomorphic trait?

Answer 3

Most fungi form hyphal growth but it also happens in holozoans and oomycetes
Not all fungi are hyphal or even yeast-like

Question 4

What are Laboulbeniomycetes?

Answer 4

Non-hyphal fungi with a determinate body plan
Has an exoskeleton and attaches itself to insects

Question 5

Why can’t the lack of flagella be used as a synapomorphic trait?

Answer 5

Blastocladiomycota and Chytridiomycota have a flagellated life stage

Question 6

What biochemical pathway isn’t found in animals but is found in fungi?

Answer 6

Fungi synthesize lysine via the alpha-aminoadipate pathway

Question 7

Through which pathway do plants, algae, and bacteria synthesize lysine?

Answer 7

Diaminopimelate pathway

Question 8

Why can’t the lysine synthesis pathway be used as a synapomorphic trait?

Answer 8

Two key alpha-aminoadipate genes are widespread in protists

Question 9

Where do the particles from endocytosis localize?

Answer 9

In the subapical collar

Question 10

What are the Golgi like in fungi?

Answer 10

Golgi are scattered throughout the cell in the form of small, perforated cisternae

Question 11

What are among some of the fastest-growing cells?

Answer 11

Filamentous fungal cells
Rates up to 1 mm in 50 minutes

Question 12

How many endocytotic vesicles need to be delivered to the cell tip to sustain such fast growth?

Answer 12

38000 vesicles

Question 13

What does SPK formation involve?

Answer 13

Cdc42, a GTPase which interacts with several other proteins (Spa2, Bud6) to form a complex called the polarisome

Question 14

What does the polarisome do?

Answer 14

Radiates actin filaments by means of forming (SepA and Bni1)

Question 15

What are the motors that deliver vesicles?

Answer 15

Kinesins
Dyneins
Myosins

Question 16

What does myosin-5 do?

Answer 16

They are outward-bound motors following actin filaments: they deliver vesicles for exocytosis as well as reinforcing the lipid rafts at the tip
Docks with exocyst protein complexes which enable vesicles to be guided to the plasma membrane

Question 17

What does myosin-1 do?

Answer 17

Appears to support endocytosis - inward-bound

Question 18

What do kinesins do?

Answer 18

Move cargo along microtubules to the plus end

Question 19

What do dyneins do?

Answer 19

Move cargo to the minus end

Question 20

What is the amount of dynein and kinesins necessary for hyphal tip growth?

Answer 20

1 dynein and 3 kinesins

Question 21

What does kinesin-1 do?

Answer 21

Hauls vesicles for exocytosis

Question 22

What does kinesin-3 do?

Answer 22

Forms early endosomes

Question 23

What happens in the SPK?

Answer 23

Switch from kinesin-dependent anterograde movement of early endosomes to retrograde movement

Question 24

What else is highly abundant in the SPK?

Answer 24

Ribosomes - mRNA may be delivered to SPK from the nucleus, perhaps by kinesin-3 for translation

Question 25

What is the vesicle supply center model?

Answer 25

Post-Golgi vesicles are gathered in an apical vesicle supply center that regulates growth by generating a gradient of exocytosis of enzymes Its active tip-ward movement determines hyphal shape and elongation rate

Question 26

What is the steady state model?

Answer 26

Polar exocytosis delivers wall-forming enzymes. Newly added wall material is noncrystalline and plastic and can be expanded by turgor pressure The wall solidifies as it progresses towards the subapex, resisting turgor pressure and shaping the hypha

Question 27

What is the amoeba-in-a-tube model?

Answer 27

A membrane cytoskeleton supports integrity of the tip and regulates tip extensibility The hyphal tip expands by the force produced by the cytoskeleton The cell wall is considered to be an extracellular matrix that confers shape to the hypha

Question 28

How has loss of phagotrophy contributed to the success of fungi?

Answer 28

Removed the requirement for a flexible cell surface membrane, allowing fungal cells to develop rigid and structurally reinforced cellular surfaces

Question 29

How has the rigid reinforcement of the cell surface contributed to the success of fungi?

Answer 29

Protects the cell against high turgor pressures, allowing cell function to flood the cytoplasm with high concentrations of solutes which allows for a fast metabolic rate and allows the cell to assert high force to penetrate and ramify into robust structures as part of their feeding processes

Question 30

How has the evolution of rigid cells contributed to the success of fungi?

Answer 30

Allows for polarized growth at the hyphal tip

Question 31

How has a shift to external digestion of complex compounds contributed to the success of fungi?

Answer 31

Coupled to active transport of processed metabolites into the cell