Phenotypic dissections of the Blastocladiella emersonii zoospore's developmental choice

[摘要] Blastocladiellaemersoniizoosporescaneitherremainactivelymotilecellsthatlackacellwallanddonotgrow,ortheycanencyst,therebylosingcellularmotilityandgainingacellwall,inpreparationforenteringthegrowthphase.Exclusivelypost-translationalcontrolsappeartomediatethezoospore'schoice,inresponsetoenvironmentalcues.Encystmentcanbeelicitedbyanyoneofavarietyofcompounds,buttheirencystmentelicitingeffectscanbeblockedby“zoosporemaintenancefactor”(ZMF).Theminimalconcentrationsofelicitorsjustyieldingmaximalpercentageencystment(intheabsenceofZMF)varyover10ordersofmagnitude.CyclicGMPisuniquelyeffectiveonlyinthepicomolarrange,about8ordersofmagnitudebelowtheeffectiverangeforcAMP.ZMF,releasedintothemediumbytheorganismduringzoosporeproduction(W.K.GottschalkandD.R.Sonneborn,1981,Exp.Mycol.5,1–14),blockspercentageencystmentinaconcentration-dependentmanner.Encystmentinitiationisaccomplishedwithin1–2minexposureofzoosporestoanygivenelicitor,inthepresenceorabsenceofZMF,suchthatanexternalelicitorisnolongerrequiredtocompleteencystment.TheencystmentblockpointmediatedbyZMFoccursafterinitiation,thusleadingtoretentionofthemotilezoosporephenotype;theblockpointispassed,andzoosporesencyst,followingremovalofexternalZMF.Certainencystmentelicitors(MnSO4,cGMP,cAMP,adenosine,divalentcationionophores)yieldbell-shapeddose-response(percentageencystment)plots;atappropriatelyhighconcentration,eachcompoundmediatesanencystmentblockpointthatoccursafterencystmentinitiationbutbeforetheZMFblockpoint.Ineachcase,theblockispassed,andzoosporesencyst,followingexternalremovaloftheblockingagent.Thelatterblockpoints,asopposedtotheZMFblockpoint,areinoperativeintheNaCl-elicitedencystmentpathway.Thedataestablishthatzoosporespossesscellularmachinerythatcanallowthemtoreassesstheirdevelopmentalchoiceaftertheencystmentalternativehasbeeninitiated.

[学科分类] 生物科学（综合）