Parasexuality in Fungi

Sex and sexuality are very common words in biology but para-sexuality is a little bit uncommon, several organisms in general and fungi in particular have the pleasure of sexuality to bring variations by beside sex. This PPT explores the beauty of para-sexuality for the academic fraternity.

1. MYCOLOGY -
PARASEXUALITY IN FUNGI
A Presentation by:
Dr. N. Sannigrahi,
Associate Professor,
Department of
Botany,
Nistarini College,
Purulia
D.B. Road, Purulia
(W.B) India

2. CONTENTS
 What is Parasexuality ?
 Occurrence of Parasexuality,
 Steps of Parasexuality
 i. Establishment of heterokaryosis,
 ii. Formation of heterozygous diploids or diplodization,
 iii. Occasional mitotic crossing over,
 iv. Haplodization
 V. Sorting of new haploid strains
 Comparison between sexual cycle & Parasexual cycle,
 Significance of Parasexuality

3. PARASEXUALITY ?
Sexualreproductionneedstwosexorgansalongwithtwonon-identical
gametesfollowedbynuclearfusion.InFungi,zygoticmeiosistakersplace
fortheformationofhaploidgametophyte,
Insomecasesinfungi,adifferentwaytodescribethebenefitsofsexual
cycle,
Thesexualitybytheaforesaidprocessistreatedasparasexualityandthe
cycleofoccurrenceiscalledparasexualcycle.Here,‘Para’means‘beside’
Sex.
FirstreportedbyGudioPontecarvoandJ.A.Roper(1952)onthebasisof
thestudyofimperfectstageofAspergillusnidulans.
Innormalevents,plasmogamy,karyogamy&meiosistakeplacein
sequencebutinparasexualcycle,theeventssomewhattakeplacebutnotin
properorderorspecifiedtime,
Itisalsocalledsomaticrecombinationbecauseinthiscase,genetic
materialexchangetakeplaceduringmitosiswithoutthepleasureofthe
developmentofdesiredsexorgans.

4. OCCURENCE
Thispleasureofsexualoccurrenceofexceptionbehaviorisfoundinmany
fungisincethisdiscoveryinAspergillusnidulans,
MostlyfoundintheclassofDeuteromycetesorFungiImperfectior
SyntheticFungiasnonormalsexualreproductiondoesnottakeplace,
SomemembersofBasidiomycets,Ascomycetesincertaincases,
SomenotablefungihavetheoccurrencelikeAspergillusfumigates,A.
oryzae,Penicilliumchrysogenum,P.expansum,P.indicum,Ustilago
vioacea,U.horedei,Piriculariaoryzae,Verticillumalboratum,Fusarium
oxysporumetc.
Thiseventisnotordinaryone,ratheritistheexceptionaloneasfaras
sexualbehaviorisconcerned.

5. PARASEXUAL PROCESS

6. STEPS OF PARASEXUAL CYCLE
AccordingtoPointecarvo(1958),parasexualcycleinA.nidulans,the
followingstepsareinvolvedinparasexualcycle.
i.Formationofheterokaryoticmycelium-EitherbyMutationor
AnastomosisorDiplodisation,
ii.Fusionbetweentwonuclei-Fusionbetweenlikenuclei&fusion
betweenunlikenuclei,
iii.Multiplicationofdiploidnuclei,
iv.Occasionalmitoticcrossingover,
v.Sortingoutofdiploidnuclei,
vi.OccasionalHaplodizationofdiploidnuclei,
vii.Sortingofnewhaploidstrains

7. MECHANISMS
Establishment of heterokaryosis -
Heterokaryosismeanstheoccurrenceofnucleiofdissimilargenotypesin
thesamecellorcytoplasm,
Thepresenceofdissimilartwohaploid(n)nucleiinthesamecytoplasmis
thepreliminaryrequirementforgeneticrecombination,
Inthesefungi,thisheterokaryoticconditionisachievedeitherby
anastomosisorsometimesbymutation,
Whatevermaybe,theheterokaryonisestablishedpriortothepleasureof
beautyofthisepisode.
FormationofHeterozygousdiploidordiplodization-
Thenuclearfusioninheterokaryoticvegetativehyphaeorcellswasfirst
reportedbyRoper,1952.
Here,thenuclearfusionbetweendissimilarnucleiresultsintheformation
ofheterozygousdiploidnuclei

8. MECHANISMS
Theheterozygousnucleithatarefairlystable,bymultiplicationand
startingoutthroughconidiagiverisetodiploidthalli,
ThediploidcoloniesarecharacterizedbyhigherDNAcontent,biggersize
conidiaandphenotypiccharactersofthecolony,
Fusionbetweenidenticalnucleiisfound,thehomozygousdiploidnucleus
formedduetothisultimatelygiverisetonon-recombinanthaploidnuclei,
suchformshavenogeneticrelevance,
Inthisheterokaryon,amixtureofthetwooriginalhaploidnucleartypesas
wellasdiploidfusionnucleiareformed.
OccasionalMitoticCrossingOver:
Verykeyeventintheparasexualcycle,
Inthisstage,geneticrecombinationtakeplace,
Crossingoverduringmitosisisararephenomenonasfirstreportedinthe
fruitflybyStern(1936),
InAspergillusnidulans,themitoticcrossingoveroccursbutwitha
frequencyof10-2pernucleardivision

9. MECHANISMS
Reciprocalexchangesbetweenhomologouschromosomesatthefour-
strandedstagewerereportedbyPitcherandRoper.Itisthecharacteristic
featureofmitoticcrossingoverthatexchangeorthechiasmataformationis
confinedtoasinglechromosomepairoutofthewholecomplementof
chromosomes.
Haplodization:
Itistheformationofhaploidnucleifromthediploidnucleusduetonon-
disjunctionofchromosomesoccurringduringdivisionofthediplod
nucleus,
Itisalsoveryexceptionalfeature,
Theformationofhaploidnucleusdoesnotundergomeiosis.Duringmitotic
divisionofthediploid(eventhehaploidcell)irregularity(non-disjunction)
duringchromosomesseparationleadstosomenucleiwith2n-1andsome
with2n+1,thereby,exhibitinganeuplodyeitherhypoploidyorhyperploids,
Suchaneuplodynucleiwithincompletemultipliesofhaploidnumbertend
tobeunstable,furtherchromosomesduringsubsequentmitoticdivisions
until2n-1&2n+1progressivelyreverttonstate.

10. MECHANISMS
Sortingofnewhaploid(n)strains:
Somediploid(2n)nucleiundergoesHaplodizationinthemyceliumandare
sortedoutbyincorporationofhaploidnucleiintheuninucleateconidia.
Someofthesehaploidstrainsaregenotypicallydifferentfromtheparent
becauseofmitoticrecombination.
Thus,theparasexualcyclehasoperatedforsometime,themyceliamay
containthefollowingtypesofnuclei:
Haploidnucleilikethoseofbothparents,
Haploidnucleiwithvariousnewgeneticrecombination,
Severaltypesofdiploidhomozygousnuclei,
Severaltypesofdiploidheterozygousnuclei.
Theparasexualcyclecloselystimulatestheeventsofsexualcycle.It
involveseverycomponentsofthesexualcyclelikeplasmogamy,
karyogamy,Haplodizationbutlittlebitofmodifiedformandwithoutany
fixedplanwithregardtotimeandspace.Butthetwoprocessesboththe
sexualandparasexualcyclegiverisetotherecombinantofhaploidnuclei.

11. COMPARISON BETWEEN SEXUALITY & PARASEXUALITY
Sr.
No.
Sexual cycle Parasexual Cycle
1. Nuclearfusiontakesplaceinthe
specializedstructure.
Nuclearfusiontakesplacerarelyin
vegetativecells.
2. Zygoteusuallypersistsonenuclear
generation.
Zygotepersiststhroughmany
mitosis.
3. Recombinationbymeiosis,crossing
overinallchromosomespair,of
reductionofchromosomenumberand
randomassortmentofnumbersofeach
chromosomepairarecharacteristicsof
thecycle.
Recombinationbyrareaccidentsof
mitosis;mitoticcrossingoverat
eventusuallyconfinedtoone
exchangeinasinglechromosome
armandHaplodizationindependent
ofcrossingoverarethefeaturesof
thiscycle.
4. Productsofmeiosiscaneasilybe
recognizedandisolated.
Productscanberecognizedbythe
applicationofsuitablegenetic
markers.

12. SIGNIFICANCE OF PARASEXUALITY
a.Itisveryimportantinindustrialprocesses,
b.SeveralfungihavinghighdegreeofindustrialapplicationbelongtoFungi
Imperfectiandthesefungioperateparasexualcycle.
c.Newandbetterstrainsoffungiareobtainedbymutationthrough
parasexualcycle,
d.Thestrainsofdesirablecharacterscanbedevelopedthroughmitotic
recombination,
e.Itcanbealsoappliedintheanalysisofgeneticandphysiological
processesofperfectandimperfectfungi,
f.Parasexualcyclehasalsobeensuccessfullyemployedinthegenetic
controlofpathogenecityandhost-rangeinseveralspeciesofFusarium.

13. PARASEXUALITY-THE BEAUTY OF SEX LIFE IN FUNGI
References:
Google for images
Introduction to Mycology & Phytopathology -Mishra & Dash
Brook Microbiology of Microorganisms-Madigan, Martinko, Bender,
Buckley & Stahl,
Botany for degree students; Fungi-Vashishta & Sinha,
A Textbook of Microbiology-Chakraborty,
Microbiology-Pelzer, Chan & Krieg,
Different WebPages to enrich content.
Disclaimer:This PPT has been designed to enrich the open source of learning.
The author does not claim any kind of financial pleasure.

14. THE SEXUAL BEHAVIOR AND ITS SCIENTIFIC BEAUTY IS
A PLEASURE TO BIOLOGISTS.
THANKS A LOT TO VISIT THIS CONTENT