A)Light-grown corn(B)Dark-growncorn(c)Light-grownbeanD)Dark-grown beanFigure 9-1
Figure 9-1
545福Red Far-redRedDarkFigure 9-2FIGURE17.2Lettuce seedgerminationisatypical photoreversible response controlledbyphytochrome.Red lightpromotes lettuce seed germination, but this effect isreversed byfar-red light.Imbibed (water-moistened)seedsweregiven alternatingtreatments ofred followed byfar-red light.The effect of the light treatment depended on thelasttreatmentgiven.(PhotosM.B.Wilkins.)Red Far-redRed Far-redRedFar-redRed
Figure 9-2
First node1212Epicotyl220Cotyledon10FIGURE17.6 Phytochrome is20most heavilyconcentrated inRootthe regions where dramaticdevelopmental changes areoccurring:theapical meristems20oftheepicotylandroot.Shownhere is the distribution of phy10tochrome in an etiolated peaseedling,asmeasured spectrophotometrically.(FromKendrickandFrankland1983.ConcentrationofphytochromeFigure 9-3
Figure 9-3
Chromophore:phytochromobilinRPrRHisapidadioB-aNC10H1HTisPrPUCis isomerThioetherlinkageGlrRed lightconvertscisto transRProR15CHisHBN-H510TransisomerHHisPfrLeuFigure 9-5Structureof thePrand Pfrformsofthechro-FIGURE17.4mophore(phytochromobilin)and thepeptideregionboundto the chromophore through a thioether linkage.The chro-mophore undergoes a cis-trans isomerization atcarbon 15inresponse to red and far-red light.(AfterAndel etal.i997.)
Figure 9-5
Chromophore-bindingdomainsIAIIAIBIIBFIGURE17.5Structureofthephytochromedimer.Themonomers arelabeled I and I.Eachmonomer consists of achromophore-binding domain(A)and asmallernonchro-mophore domain (B).The moleculeas a wholehas anellipsoidal rather than globular shape.(After Tokutomi et al.1989.)Figure 9-5-1
Figure 9-5-1
(A)PhytochromechromophoreCysHO,CCO,HH.CSHHHBDANNNHHHFigure 9-5-2(B)PhytochromeproteinSer-TKD2TKD1ChromophoreCABN
Figure 9-5-2
(C)Absorption spectra of PR and PrR0.8Pr0.6eoLo0.40.2Figure18.23Structure and func-tion of phytochromes.O1(A)Thephytochrome300500600700800400chromophoreis a tetra-Wavelength (nm)pyrrole that binds to thephytochromeprotein.(B)TheCtermini ofplant phytochromesmay(D)Phytochrome activitiescontain two distincttransmitter kinase do660nmmains,TKD2and TKD1.DevelopmentalPRPFR(C)Absorptionspectraresponses730nmof PR and PrR showpeaks for red (660 nm)and far-red (730 nm)light,respectively.660nm(D)Phytochromes canSeedexist as either of twogermination730nminterconvertibleforms.Isolatedphytochromesin a concentrated solu-660mmtion can undergo re-versible changes in730nmabsorbance induced byillumination with redOr far-red light. Theselight-induced structuralGreeningofchanges are coincidentseedlingwithphysiological andFigure 9-5-3developmental changesinducedbyredlightorblocked byfar-red light
Figure 9-5-3
NUCLEUSPLASTIDPHYmRNAPhytochromobilinPhytochromeapoproteinFigure 9-6RedPhytochromePfrPrholoproteinFar-redCYTOSOLFigure 17.6Phytochromobilinis synthesizedinplastidsandreleased into the cytosol,where it assembles with the phy-tochromeapoprotein.(AfterKendricketal.1997.)
Figure 9-6
(A)BacterialphytochromeRed lightChromophoreSensor proteinHisInputTransmitter1ResponseregulatorproteinATPAspOutputReceiverChromophore?HisinputTransmitter?+1.AfterreceivingasignalfromtheinputASPOutputReceiverdomain,thetransmitterdomain.otthesensorproteinautophosphorylatesahistidine.2,Thephosphorylated sensorproteinOutputphosphorylatestheresponseregulatorsignalproteinatanaspartate.3.Thephosphorylatedresponse regulatorstimulatestheresponsePlantphytochrome(B)Red lightChromophoreSerH2NKinase.domain-COOH1Phytochrome1.PhytochromeisATPautophosphorylated2on serine.ChromophoreeH2NSerKinase domainCOOHFIGURE17.21Phytochromeisanautophospho-rylating protein kinase.(A)Bacterial phy--.-tochromeis anexample ofa two-componentsignalingsystem,in whichphytochromefunc-Ptionsas a sensor protein that phosphorylates aresponseregulator(seeChapter14on theweb2.Phytochromemaysite),(B)Plantphytochrome is an autophospho-Figure 9-11phosphorylateotherrylating serine/threoninekinasethatmayphos-proteins.phorylate other proteins (X)
Figure 9-11
COPCYTOPLASMLight@Dark+DADarkPSK1COP1LightRedFarred10HYSSPAT12)lighttightPSK1eLightDark?XATPELight1HY5PfrAPfrAPDPfrAdegradation?6T?④Light-regulatedCOPIDETIFUSgene expressionproteasomeXCGMPG-SproteinCAMYCaz4?2NUCLEUS1Light8ATP6pfrB?PfrBPPfrB?NDPK2PIFLightRedFarredlightlight7NDPK2PrBRedlightconvertsPrAandPrBtotheirpfrforms.ThePfrformsofphyAandphyBphytochromecan.autophosphorylate②Activated.PfrAphosphorylatesphytochromekinasesubstrate1(Pks1).??ActivatedPfrAandPfrBmayinteractwithG-proteins.cGMp,calmodulin(cAM),andcalcium(Caz+)mayactivatetranscriptionfactors(xandY)?6ActivatedPfrAandPfrBenterthenucleus.PfrAand PfrBmayregulatetranscriptiondirectlyorthroughlnteractionwithphytochrome?interactingfactor3(PiF3).Figure 9-12Nucleosidediphosphatekinase2(NDpK2)isactivatedbyPfrB.B?Inthedark,cOp1entersthenucleusandsuppresseslight-regulatedgenes,tnthedark,Cop1,anE3ligase,ubiquitinatesHY5.HY5isdegradedwiththeassistanceoftheCOp/DET/FUsproteasomecomplex:in the dark,inthelight,COp1 interactsdirectlywithSpA1andisexportedtothecytoplasm.2Summarydiagram oftheknownfactorsinvolved in phytochrome-FIGURE17.22regulatedgeneexpression.Itislikelythatadditional sharedandphytochrome-specifiepathways wili beuncovered as moresignaling intermediatesare identified.(AfterSharma 2001.)
Figure 9-12