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BOT 306 > Vegetative Incompatibility and Sex in Fungi > Flashcards

Vegetative Incompatibility and Sex in Fungi Flashcards

1
Q

What is a prerequisite to anastomosis?

A

Somatic fusion

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2
Q

Why must somatic fusion be closely regulated?

A

So that the physiological and genetic advantages of heterokaryosis can be realized without hazard

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3
Q

What are the advantages of somatic fusion?

A

Functional diploidy

Mitotic recombination via parasexuality (important in clonal species)

Proceed to sexual processes in basidiomycetes

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4
Q

What are the hazards/risks of somatic fusion?

A

Risk of exposure to contamination with alien genetic information

Infection agents can be transmitted

Mycoviruses

Greedy genomic elements

Senescence plasmids

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5
Q

What is a locus?

A

A specified location on a chromosome

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6
Q

What is non-self-recognition mediated by?

A

Heterokaryon incompatibility

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7
Q

What is heterokaryon incompatibility also called?

A

Vegetative compatibility

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8
Q

What are two specific ways that nonself-recognition is mediated?

A

Alternate alleles at a single locus (allelic HI)

Alternate alleles at more than one locus (non-allelic HI)

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9
Q

What is a V-C group?

A

Individuals with matching alleles belong to the same V-C group

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10
Q

How many loci can be involved in a V-C group?

A

Up to 10 loci, a mismatch at any one can lead to HI

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11
Q

Individuals in the same V-C group can have the same or opposite mating types, how does this affect growth after fusion?

A

Same mating type = growth after fusion is normal

Opposite mating type = growth is slowed

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12
Q

What do mismatched het genes result in?

A

Barrages

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13
Q

What is a barrage?

A

A line or zone of demarcation that develops at the interface where two genetically different fungi meet

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14
Q

What do het genes regulate?

A

STAND proteins

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15
Q

What are STAND proteins?

A

Signal transducing ATPases with numerous domains

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16
Q

What do the up or downregulation of STAND proteins lead to?

A

Massive expressional changes

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17
Q

What do fungal STAND proteins contain?

A

a PCD switch = a het domain that induces programmed cell death

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18
Q

What does the co-expression of any incompatible het genes lead to?

A

PCD

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19
Q

How is the PCD phenomenon contained?

A

by walling off the affected area or closing septal pores

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20
Q

What is the difference between VC/HI and controlled mating?

A

Vegetative compatibility controlled by self/non-self recognition genes: cytoplasm to mingle must be as similar as possible

Mating controlled by mating-type genes: maximal advantage when nuclei are as different as possible

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21
Q

What does PCD not extend to?

A

Sexual plasmogamy

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22
Q

In what situation does PCD not occur?

A

When a trichogyne is united with a spermatium of the opposite mating type (compatible) but incompatible V-C group

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23
Q

What happens when there is no V-C, but matching mating types?

A

Perithecia in barrage

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24
Q

What is mating controlled by in fungi?

A

One MAT locus

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25
Q

What is the MAT locus like in ascomycetes?

A

The alleles are completely different pieces of DNA; they are called idiomorphs

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26
Q

How are mating types in ascomycetes referred to?

A

mating types A and a or a and alpha

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27
Q

What happens if the idiomorphs at the MAT loci differ and what type of fungi use this system?

A

Successful mating, heterothallic fungi

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28
Q

When does mating fail in heterothallic fungi?

A

If strains are of identical mating type

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29
Q

What are homothallic fungi?

A

Fungi can reproduce sexually without another individual

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30
Q

What is the 2-way arrangement of MAT idiomorphs called?

A

A bipolar mating system

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31
Q

How many alleles/idiomorphs are possible in ascomycetes?

A

Two

32
Q

How many alleles are possible with basidiomycetes with a bipolar mating system?

A

Many alleles are possible

33
Q

Many basidiomycetes have what breeding system?

A

A tetrapolar mating system
Also called bifactorial because two loci are involved

34
Q

What is non-outcrossing?

A

Self-fertilization of a haploid homokaryon results in production of identical homokaryotic progeny

35
Q

What is the result of non-outcrossing?

A

Clonal propagation - purely asexual reproduction

36
Q

What is outcrossing?

A

Conjugation between different parental haploid genotypes following karyogamy and meiosis which results in the production of non-identical haploid homokaryotic progeny

37
Q

What are two possible types of outcrossing?

A

Outbreeding and inbreeding

38
Q

What is outbreeding?

A

Conjugation between haploids from different spore sources (non-siblings)

39
Q

What is inbreeding?

A

Conjugation between haploids from the same spore source (siblings)

40
Q

What is inbreeding potential?

A

The probability that a randomly encountered sibling will be compatible
It can also be calculated from the ratio of offspring

41
Q

What is outbreeding potential?

A

The probability that a randomly encountered unrelated individual will be compatible

42
Q

What affects the inbreeding and outbreeding potential?

A

The number of loci and alleles

43
Q

What are the inbreeding and outbreeding potentials of ascomycetes?

A

In: 50%
Out: 50%

44
Q

What are the inbreeding and outbreeding potentials of unifactorial basidiomycetes?

A

In: 50%
Out: nearly 100%

45
Q

Why is the outbreeding potential in basidiomycetes nearly 100%?

A

Because >2 mating types are available in the population

46
Q

What are the inbreeding and outbreeding potentials of bifactorial basidiomycetes?

A

In: 25%
Out: nearly 100%

47
Q

What makes the outbreeding potential closer to 100%?

A

The more A and B alleles a population contains

48
Q

What is homothallism?

A

In some species, cells are universally compatible, including among clonemates
Does not result in actual recombination
Just an umbrella term

49
Q

What is primary homothallism?

A

The presence of both MAT idiomorphs within a single genome allows the production of eight uninucleate ascospores identical to the parental cell

50
Q

What is pseudohomothallism?

A

Self-fertility = the result of packing of 2, opposite mating type nuclei in a single cell
Independent sexual reproduction = 4 binucleate ascospores

51
Q

What is bidirectional mating type switching?

A

Cells of either mating type undergo mitosis to form two identical cells, one of which is then able to switch to the opposite mating type
This leads to a mixed colony capable of sexual reproduction via functional heterothallism

52
Q

Why is mating type switching bidirectional?

A

Since any one of the offspring spores can switch mating type

53
Q

Is S. cerevisiae homo or heterothallic?

A

Has been reported to be either
Every individual contains both Mat-1-1 and Mat1-2 idiomorphs

54
Q

What does the S. cerevisiae Mat1 locus look like?

A

Flanked by two mating-type-like loci
The first MTL locus (HMLa) contains a MAT1-1 sequence
The second MTL locus (HMRa) contains a MAT1-2 sequence
Both are silent due to tightly wound heterochromatin

55
Q

What is mating type switching regulated by in S. cerevisiae?

A

Another gene altogether
An HO endonuclease recognizes MAT1 and excises it; the neighboring locus is used as a template for the construction of a new MAT locus which allows switches in both directions in the lifetime of the colony

56
Q

How does mating type switching work in S. cerevisiae?

A

Mating-type genes are present at two additional silent loci on the genome
A ds DNA break at the MAT locus can result in DNA from a silent locus being copied to the MAT locus

57
Q

What is unidirectional type switching?

A

Cells of the hyphae of one mating type are able to switch mating type, producing a mixed mating type culture capable of sexual reproduction
The other mating type is unable to switch and thus requires the presence of a second individual to undergo sexual reproduction

58
Q

What are fertility and spore size linked to?

A

Mating type

59
Q

What is the fertility like in large and small spores?

A

Large = self-fertile
Small = self-sterile

60
Q

When are individuals from small spores fertile?

A

Only if cultured together with individuals from large spores

61
Q

What do individuals produced from self-fertile large spores give rise to?

A

Half large and half small spores

62
Q

What spore types must be able to switch?

A

Large spore type must be able to switch to small spore type but not vice versa

63
Q

What is unisexual reproduction?

A

Cells of the same mating type are able to interact and produce sexual spores regardless of the absence of an opposite mating type partner

64
Q

What do many Neurospora strains exhibit?

A

Primary homothallism

65
Q

Which is the only Neurospora species that has only one MAT idiomorph?

A

N. africana

66
Q

What are the characteristics of N. africana?

A

It is self-fertile
Transformation of related heterothallic strains with the N. africana MAT idiomorph does not result in self-fertility
MAT idiomorph is probably not solely responsible for sexual reproduction

67
Q

What is a benefit gained from homothallism?

A

Increased number of available mates

68
Q

What is a benefit lost from homothallism?

A

Deleterious mutations are not eliminated by recombination

69
Q

What is a benefit not lost from homothallism?

A

Processes that kick in during sexual cycle, such as genome editing defences or silencing of unpaired DNA, are kept in place

70
Q

What is the cost of homothallism?

A

Machinery and energetic costs of sex are maintained

71
Q

What is the Buller phenomenon?

A

Heterothallism by nucleus donation
He + Ho mating = heterokaryon donates nucleus
Also Ho + Ho mating

72
Q

What is an application of the Buller phenomenon?

A

Mycoculture, especially for food like button mushrooms

73
Q

How does the Buller phenomenon in mycoculture work?

A

Parental strain A goes through fructification and those spores are suspended in a grain spawn of homokaryon
The spores and homokaryon are inoculated in the compost of 4 culture trays
Then there is the fructification of hybrids sporocarps AxB

74
Q

How is genetic diversity achieved in parasexuality?

A

Mitotic crossing over
It rarely occurs and comes about through the ability of nuclei to form somatic diploids in fused, heterokaryotic hyphae

75
Q

Is there true asexuality in fungi?

A

Some fungi lack a known sexual stage
Cryptic sex?
Some asexual fungi can have functional MAT genes, so maybe other genes are essential for mating that these fungi lack

BOT 306 (16 decks)

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