Lecture'17'Bio'200''Fungi:'• Very'different'from'the'organisms'we'have'seen'so'far'• Hard'to'study'because'often'not'visible'unless'they'are'sexually'reproducing'• Hard'to'study'over'a'long'period'of'time'• Even'sexual'reproduction'can'be'absent'for'generation'• Most'of'the'fungi’s'life,'we'cant'observe'• Fairly'little'we'know'about'the' g roup.'• A'fungi'has'traits'that'are'almost'plantIlike'• Unable'to'move'• Unique'life'cycles'(with'haploid'stages)'• Were'grouped'with'plants,'but'we'now'know'they'make'up'a'monophyletic'clade'• Fungi'are'closer'related'to'animals'then'they'are'to'plants.''• In'the'group'Opisthonkonts.'• Animals,'fungi,'and'chaonoflagellates'make'up'the'group'Opisthinkonts.''• Very'variable'group'of'organisms,'but'genetically'they'are'fairly'closely'related.''• Humans'aren’t'that'distantly'related'to'fungi'• The'common'ancestor'of'fungi’s,'were'single'celled'eukaryote'• A'ton'of'fungi'that'show'an'amazing'diversity,'shows'up'after'a'rain'fall'especially.'• Some'are'poisonous,'some'use'in'our'food,'and'some'we'don’t'see'at'all.''• Lots'of'DNA'evidence'and'how'they'are'related.''• 6'groups'of'fungus.'''Six'basic'traits'of'Fungi:'• Most'fungi'have'a'number'of'cell'types'o Unicellular'(can'be'flagellated)I''! found'in'most'of'the'fungal'groups'and'they'are'all'called'Yeast.'Yeast'refers'to'a'lifestyle,'not'a'taxonomic'group.''o MulticellularI''! Ex:'earth'star'fungus.''! Can'have'unicellular'stages'! They'are'filamentous'! Their'vegetative'portion'is'called'a'mycelium.'! The'mycelium'is'composed'of'long'strands'or'tubular'filaments'that'are'called'hyphae.'! HyphaeI'usually'long'chains'of'cell'like'structures'that'are'joined'end'to'end'! The'cell'like'structures'can'be'divided'by'cross'pieces'that'are'called'Septa.'! Septa'are'not'usually'complete'barriers,'they'often'have'pores'in'them'that'allows'free'transfer'of'cytoplasm'! Even'with'the'septa'present,'most'hyphae'can'be'considered'single'long'multinucleate'cells.''! Fungi'that'have'hyphae'receptor'are'ca l led'Septate'Fungi'! Some'fungi'that'don’t'have'these'septa,'that'are'separating'these'cell'like'structures.'They'are'called'Coenocytic.'! The'fact'that'the'coenocytic'fungi'exists'indicates'that'the'cell'separation'by'the'septate'is'not'really'important'for'the'fungi.''! Products'that'are'synthesized'or'absorbed'by'the'fungi’s'can'quickly'stream'through'the'body,'to'the'actively'growing'tips'to'the'hyphae.'This'allows'fungi'to'grow'very'rapidly'when'water'or'food'is'abundant.''! This'is'why'we'can'see'mushrooms'pop'up'in'the'yeard'overnight'when'there'is'rain'! When'hyphae'are'joined'together,'it'is'called'a'mycelium.''! Through'the'mycelium,'that'the'fungus'absorbed'the'nutrients'from'its'environment.''! A'portion'of'the'mycelium'in'some'fungal'groups'can'take'form'of'a'reproductive'body'such'as'a'mushroom'or'other'fruiting'bodies.'''• Fungi'have'cell'walls'with'chitin'o Chitin'is'really'what'gives'fungal'cells'their'structure'o 'The'same'material'that'insects'use'to'make'their'hard'exoskeletons.'• Some'fungi'have'Dikaryon'stages'o Fungal'hyphae'(cells)'they'can'house'one'or'two'or'many'nuclei.''o They'don’t'have'a'septate'separating'the'hyphae.''o They'can'hold'a'lot'of'nuclei'in'their'cells'o Distinguishes'fungi'from'plants'and'animals.''o 'DikaryonI'two'nuclei'o Usually'formed'when'two'haploid'mating'strings'fused'and'then'creating'these'dikaryotic'cells.''o Both'haploid'so'they'exist'independently'o Although,'both'nuclei'are'haploid,'they'are'both'protected'from'the'dangers'of'being'truly'haploid'o 'Both'their'genomes'are'being'transcribes.'This'protects'them'from'lethal''recessive'mutations'that'would'be'unmasked'in'a'true'haploid'organism.'o DikaryonsI'they'are'rarely'distinguishes'between'male'and'female'structures.'But'even'between'male'and'female'individuals.''o Instead'in'a'given'species,'there'are'multiple'mating'types.'These'mating'types'differ.'o 'Individuals'with'the'same'mating'types'cannot'mate'together'o However,'individuals'with'different'mating'within'the'same'species'types'can.''o The'same'mating'types'cannot'mate'because'it'prevents'self'fertilization'• Fungi'undergo'nuclear'mitosis'o The'cell'is'not'the'relevant'unit'of'reproduction'o The'cells'do'not'divide'in'mitosis'o The'nucleus'divides'without'breaking'down'the'nuclear'envelope.''o The'nuclear'envelope'pinches'off'2'nuclei'at'the'end'of'division'• Many'Fungi'have'both'sexual'and'asexual'reproduction'o Sexual'reproduction'is'rare'in'some'fungi,'but'is'common'in'other'fungi.'o When'two'haploid'strains'fuse'togetherI'sexual'reproduction'o Meddling'of''two'genomes'in'a'new'individualI'sex'in'the'fungi'o In'plants'and'animals,'when'two'haploid'cells'fuse,'we'get'the'zygoteI'the'product.'The'zygote'is'2n'o In'some'groups'of'the'fungi,'we'have'this'dikaryon'stage,'this'means'that'we'have'1N+1N,'because'the'haploid'nuclei'function'independently.''o Sometime'this'stage'is'very'brief,'followed'by'nuclear'fusion'or'fertilization''o In'other'species'the'dikaryon'form'can'be'the'dominant'life'stage,'with'a'very'brief'diploid'stage'after'fertilization'and'before'spore'productionI'meiosis.''o Fungal'sexual'reproduction'is'done'throu g h'spores'that'function'like'haploid'gametes,'often'dispersed'by'wind.'o When'spores'land'in'an'appropriate'place,'they'germinate'and'produce'more'fungus.'The'spores'are'haploid.''o Then'the'fungal'asexual'reproduction,'is'often'done'by'spores'in'the'multicellular'fungi.'o Spores'that'have'arisen'by'meiosis'can'undergo'mitosis.'They'grow'into'sporangia'and'produce'more'spores'via'mitosis.''o Environmental'conditions'determine'which'mode'of'reproduction'will'take'place'at'a'given'time.''o The'mode'and'state'of'sexual'reproduction'is'one'of'the'most'critical'characters'for'defining'species'and'phylogenetic'placement'of'the'fungi.'These'stages'are'often'very'rare,'they'can'occur'very'quickly'and'therefore'they'can'be'fairly'hard'to'observe.'o In'the'mushrooms,'only'the'mushrooms'themselves'produce'spores.'But'they'often'aren’t'seen'for'months'or'even'years'growing'asexually'underground.'o This'made'the'fungal'phylogeny'hard'to'establish.''''''''''''''''''• Fungi'are'heterotrophs'that'absorb'nut rien ts.'o The'fungi'are'heterotrophs'that'absorb'nutrients'o They'use'external'digestion,'like'the'oomycetes'(protists).'(EX:'Mycelium'on'decomposing'log')''o
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