Shoot meristem self-organization and identitySlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Shoot meristem self-organization and identityVegetative shoot apical meristem (SAM)(from Long et al., 1996, Nature 379: 66-69)Wild-type shoot apex shootmeristemless apexGene expression in embryonic SAMWUSCHEL (WUS) SHOOTMERISTEMLESS (STM)(from Laux et al., 1998, Cell 95: 805-815)wuschel mutant(from Laux et al., 1998, Cell 95: 805-815)Wild typeGene expression in embryo SAMWUSCHEL (WUS) SHOOTMERISTEMLESS (STM)(from Laux et al., 1998, Cell 95: 805-815)WUS expression in adult shoot meristems(from Laux et al., 1998, Cell 95: 805-815)(from J. C. Fletcher et al., Science 283, 1911 -1914 (1999)) Wild type clavata3 mutant clv1 and clv3 mutants look similarclavata mutants have enlarged meristemsExpression of CLV1 in Arabidopsis inflorescence shoot meristemClark et al., Cell 89: 575-585 (1997)CLV3 (A-D) and CLV1 (E) expression (from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))CLV3 expression in a clv1 mutant meristem (from J. C. Fletcher et al., Science 283, 1911 -1914 (1999))Model for CLV3 peptide signalingSupport for model:In clv mutant, WUS expression domain expands.clv wus double mutants resemble wus single mutants. If you overexpress WUS, CLV genes are activated and new meristems form.Model for shoot apical meristem (SAM) maintenanceSarkar et al. (2007) Nature 446: 811-814WOX5 is similar in sequence to WUSCHEL.WOX5 is expressed in the root quiescent center.Similar regulation in shoot and root meristemsSarkar et al. (2007) Nature 446: 811-814Root cap stem cells differentiate in a wox5 mutant.Similar regulation in shoot and root meristemsInflorescence meristem:Makes flowers instead of leaves and branchesStem elongates moreVegetative SAMInflorescence SAMFlower meristemsLeaves, branches (lateral meristems)Sepals, petals, stamens, carpelsInduction of floweringShoot meristem identitiesVegetative SAM (indeterminate)Inflorescence SAM (indeterminate)Flower meristems (determinate)Leaves, branches (lateral meristems)Sepals, petals, stamens, carpelsInduction of floweringShoot meristem identitiesVegetative shoot apical meristem (SAM)Flower meristemsShoot apical meristem (SAM)Flower meristem FlowerArabidopsis flowerSepalStamenGynoecium(fused carpels)PetalVegetative SAM (indeterminate)Inflorescence SAM (indeterminate)Flower meristems (determinate)Leaves, branches (lateral meristems)Sepals, petals, stamens, carpelsInduction of floweringShoot meristem identities1 2 3 44 sepals4 petals6 stamens2 carpelsWhorlsArabidopsis mutants with altered flowersapetala1apetala1cauliflowerpistillataWild typeagamousVegetative SAMInflorescence SAMFlower meristems Meristem identity genes (LFY, AP1, CAL)Leaves, branches (lateral meristems)Sepals, petals, stamens, carpelsInduction of floweringShoot meristem identitiesleafy mutants:partial conversion of flowers to lateral branches and leavesleafy mutant flowers have no petals or stamensleafyWild typeLEAFY is expressed throughout the flower meristem(from Weigel et al., 1992, Cell 69: 843-859)apetala1 mutant flowers lack sepals and petals and have a new flower where a petal should beWild typeapetala1Flowers are converted intoleafy shoots in leafy apetala1 mutantsFlower meristems behave like inflorescence meristems in the apetala1 cauliflower double mutantap1 calap1 calFig. 20.41ap1 calWhy did they call this mutant cauliflower?Vegetative SAMInflorescence SAMFlower meristemsLeaves, branches (lateral meristems)Sepals, petals, stamens, carpels Organ identity genes (AP1, AP2, PI, AP3, AG SEP1, SEP2, SEP3)Induction of floweringShoot meristem
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