Lecture 17: Regulation of floral organ identityRead 759-764; 776-780Fig. B1, B2, B5, B18, B19Fig. B.1Advantages of studying Arabidopsis thaliana(Arabidopsis: same family as mustard and cabbage)Small in sizeFast life cycle (6 weeks per generation)Large amount of seeds (10,000-40,000/plant)Self fertilizationEasy to growFive chromosomesLittle repetitive DNA25,498 genesEasy transformationGenome has been completely sequencedFig. B.5Rosette leaf20 shoots InflorescenceIM1234Inflorescence Meristem (IM)Arabidopsis plantThe ABC’s of Arabidopsis thaliana flower developmentCSEPAL STAMEN CARPELPETALBAwhorl 1 whorl 2 whorl 3 whorl 4C class: AGAMOUS (AG)AG is a MADS box transcription factor AG specifies stamen and carpel identity AG represses sepal and petal identitiesAG controls floral meristem determinacyExpressed in whorls 3 and 4SEPAL PETALNEW FLOWERPETALBAwhorl 1 whorl 2 whorl 3 whorl 4CSEPAL CARPELAwhorl 1 whorl 2 whorl 3 whorl 4SEPALCARPELB class: PISTILL!ATA (PI)APETALA3 (AP3)MADS box genesSpecifies petal and stamenExpressed in whorls 2 and 3Heterodimerize with each other in vitroCBract (fl) STAMEN CARPELBwhorl 1 whorl 2 whorl 3 whorl 4A class: APETALA1 (AP1)MADS box proteinMeristem identity specification:activate floral homeotic gene expressionOrgan identity specification:specifies sepal and petal identityEarly expression: in the entire floral meristem Later expression: in whorls 1 and 2CSTAMEN CARPELSTAMENBwhorl 1 whorl whorl 3 whorl 4A class: APETALA2 (AP2)AP2 encodes a novel type transcription factorwith two 68 aa. AP2 domainsAP2 specifies sepal and petal developmentAP2 negatively regulates AGExpressed in all four whorlsCARPELacbcabc•MADS box (56 aa.): highly conserved domain required for DNAbinding and dimerization.•I (31-37 aa.): an intervening region with dimerization function andspecificity•K box (66 aa.): protein-protein interaction domain•COOH (54-98 aa.): transcription activation domain in AP1MADS proteins bind cArG box (CC(A/T)6GG) in vitroFig. 19.19AP2 domain: a DNA binding domainNole-Wilson and Krizek, Nucleic Acid Research vol 28, 4076-4082, 2000A, B, C gene mRNA expression pattern revealed by in situ hybridization AP1 AP3 AG35S::Bc mutant35S::Ba mutant35S::PI35S::AP3Fig. B.2“Revisionist” ABC Model 2000ABCEpetall stamen carpelsepalSEP1 (AGL2), SEP2 (AGL4), SEP3 !(AGL9) = E classMADS box proteins (most similar to AP1)Have redundant functionSingle mutants show subtle phenotypeTriple mutant show flower phenotype similar to bc double mutantSEP1,2,3:expressed in whorls 2-3 (SEP 1,2 also in whorl1 in young flowers)Interact with B and C proteins based on yeast two-hybrid assayPelaz et al., Nature 405, 200-203, 2000A+B+E: PetalB+C+E: StamenC+E: CarpelA+?: SepalHonma and Goto, Nature 409, 525-529, 200135S::AP335S::PI35S::SEP335S::AP335S::PI35S::AP1i, j, p35S::AP335S::PI35S::AG35S::SEP3q35S::AP335S::PI35S::AGBox 19.2 (text
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