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ORGANOGENESI: DIFFERENZIAMENTO DEI PRIMORDI FOGLIARI.

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Presentazione sul tema: "ORGANOGENESI: DIFFERENZIAMENTO DEI PRIMORDI FOGLIARI."— Transcript della presentazione:

1 ORGANOGENESI: DIFFERENZIAMENTO DEI PRIMORDI FOGLIARI

2 Le foglie si formano nello sviluppo post-embrionale Germination Embryonic development zygote Cotyledons (embryonic leaves) Embryo inside seed

3 Post-embryonic development True leaves Cotyledons (embryonic leaves)

4 Sono formate dal meristema apicale del germoglio (SAM) Germination zygote SHOOT APICAL MERISTEM Leaf formation True leaves

5 Il SAM si forma durante lembriogenesi Laux, T, Jurgens, G. (1997) Plant Cell 9: TOP DOWN Apical Basal Shoot apical meristem

6 Reprinted by permission from Macmillan Publishers, Ltd: NATURE. Long, J.A., et al., 379: 66-69, copyright 1996.NATURE Dopo la germinazione il SAM forma le foglie Cotyledons Leaves Cotyledons Leaves Post-embryonic leaf formation Shoot apex at germination

7 diversi stadi nello sviluppo dei primordi Organogenesi: poche cellule negli strati L1 e L2 nella zona periferica acquistano lidentità di iniziali (founder cells) della foglia. Cominciano a dividersi più rapidamente delle cellule circostanti e formano una zona distinta dal resto del doma (primordio). Sviluppo di differenti regioni nella foglia: regioni dei primordi acquisiscono lidentità delle diverse parti della foglia. Tre assi di sviluppo: adaxiale/abaxiale; prossimale/distale; mediale/laterale Differenziamento di cellule e tessuti: Con la crescita della foglia cellule e tessuti si differenziano: L1 epidermide; L2 mesofillo; L3 elementi vascolari e cellule della guaina del fascio

8 DIVISIONI CELLULARI NELLA FORMAZIONE DEL PRIMORDIO (arabidopsis) divisioni periclinali nello strato più interno della tunica divisioni periclinali anche negli strati meno interni della tunica e divisioni meno orientate divisioni anticlinali nelllo strato esterno della tunica per formare il protoderma

9 Le foglie in formazione hanno una loro polarità intrinseca Leaf Cot Peripheral Central

10 Assi di asimmetria nella foglia

11 La polarità è evidente fin dagli stadi iniziali PeripheralCentralAdaxialAbaxial The adaxial side is towards the center of the plant

12 In quale posizione si formano sul germoglio? (fillotassi) AlternateOpposite WhorledSpiral

13 Alternata Candela, H. et al. (2008) Plant Cell 20: ; Itoh, J.-I., et al. (2000) Plant Cell 12: One leaf at a time, 180° apart, as in rice or other grasses. TEM of rice apex Cross section of rice apex

14 Opposta Two at a time, 180° apart at each node. Sometimes pairs alternate by 90° at successive nodes.

15 Verticillata Three or more leaves at each node, as in the horsetail (Equisetum). Photos courtesy of tom donaldtom donald

16 Spiralata In most plants, such as this succulent, leaves form in a regular spiral pattern. Photos courtesy of tom donaldtom donald

17 spiralata 137° In plants with spiral phyllotaxy, leaves form at about 137° apart.

18 Spiral phyllotaxy

19

20 A line through sequential leaves makes a spiral. Spiral phyllotaxy

21 The NEXT leaf to form is called the Incipient primordium (I 1 ). I1I1 Spiral phyllotaxy

22 The one that will form after that is called I 2 ….etc. I1I1 I2I2 Spiral phyllotaxy

23 Fillotassi spiralata in apice di tabacco Poethig, R.S. and Sussex,I.M. (1985) The developmental morphology and growth dynamics of the tobacco leaf. Planta 165: Copyright (1985) Planta. Reprinted with kind permission of Springer Science+Business Media. I1

24 Cosa determina la posizione del primordio incipiente? Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development Surgical experiments demonstrate that leaf placement is determined by pre- existing primordia

25 I2 This tomato apex shows the positions of several primordia (P) and incipient primordia (I). Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

26 P3P3 P2P2 P1P1 I1I1 I2I2 This tomato apex shows the positions of several primordia (P) and incipient primordia (I). The expected position for I 3 (*) can be found by tracing the spiral. I2 Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

27 P3P3 P2P2 P1P1 I1I1 I2I2 I 1 (shown in black) was surgically isolated from the rest of the meristem, by cutting along the red line. Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

28 P3P3 P2P2 P1P1 I1I1 I2I2 Two days later, the apex was examined. Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

29 P3P3 P2P2 P1P1 I1I1 I2I2 I3I3 Instead of emerging at its expected position (star), I 3 shifted towards I 1. This experiment shows that I 1 influences I 3 position. Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

30 P3P3 P2P2 P1P1 I1I1 I2I2 I3I3 Positions of I 2 and I 3 ; older leaves have been cut away. Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

31 The older primordia control the placement of the incipient primordia. P3P3 P2P2 P1P1 I1I1 I2I2 I3I3 What kind of signal or information is involved?

32 Lauxina è coinvolta nella formazione del primordio Reprinted from Current Opinion in Plant Biology, 8 (1), Byrne, M.E., Networks in leaf development, , Copyright (2005), with permission from Elsevier. Wild-type Arabidopsis shoot apex. The meristem is covered by the leaves it has produced.

33 Lauxina è coinvolta nel determinare la posizione del primordio The apex of the pin1 mutant is bare – it fails to produce lateral organs. meristem Reprinted from Current Opinion in Plant Biology, 8 (1), Byrne, M.E., Networks in leaf development, 59-66, Copyright (2005), with permission from Elsevier ; Reinhardt D et al., (2000) Plant Cell 12: Wild-type Arabidopsis shoot apex pin1 shoot apex

34 The pin1 mutant is defective in the transport of auxin. IAA NHNH O OH

35 Auxin transport pH 7pH 5 IAAH Auxin (IAA) is a weak acid. At the low pH of cell walls, it is protonated and uncharged (IAAH), allowing it to move through the plasma membrane. Cell wall Cytoplasm

36 Auxin transport IAA- pH 7pH 5 IAAH In the less acidic cytoplasm, it loses the proton, becomes charged (IAA-), and cannot exit the call by diffusion through the plasma membrane. Cell wall Cytoplasm

37 Auxin transport IAA- pH 7pH 5 IAAH PIN1 protein Auxin efflux through PIN1 The PIN1 protein is an auxin efflux carrier, transporting charged auxin back out of the cytoplasm. IAA-

38 Auxin transport The subcellular localization of PIN proteins can be polar and coordinated between cells, causing directed auxin transport. In this diagram, the accumulation of PIN1 to the right of each cell causes a net flow of auxin towards the right. Net flow of auxin IAA- pH 7pH 5 IAAH

39 Un massimo localizzato di auxina è richiesto per lorganogenesi Reinhardt D et al., (2000) Plant Cell 12: Applying a spot of exogenous auxin (shown as a red blob) stimulates outgrowth of primordium in the pin1 mutant.

40 38 hours after application4 days after application Reinhardt D et al., (2000) Plant Cell 12:

41 IAA- pH 7pH 5 IAAH Conclusion - Auxin transport and a local auxin maximum contribute to organ initiation. This conclusion is supported by imaging PIN1 distribution in living plants.

42 GFP PIN1 GFP Green fluorescent protein (GFP) emits green light when excited by blue light. Emitted light A proteins position within a cell can be determined by making a fusion protein of it with GFP, and then looking for GFP fluorescence. Visualizing PIN1 localization Excitatory light

43 PIN1pro PIN1 GFP mRNA Fusion protein GFP PIN1 Reporter gene in the nucleus Insertion into membrane PIN1 Translation Visualizing PIN1 localization GFP

44 Using a confocal laser scanning microscope, PIN1:GFP protein distribution can be imaged in the shoot apical meristem. In this image, the green lines show the position of PIN1:GFP at cell membranes. PIN1 GFP Reproduced with permission - Development Gordon, S.P., Heisler, M.G., Reddy, G.V., Ohno, C., Das, P., Meyerowitz, E.M. Development, 2007, 134 (19): Development Visualizing PIN1 localization PIN1pro PIN1 GFP mRNA

45 La distribuzione di PIN1 è dinamica durante lorganogenesi PIN1:GFPPositions of primoridia and incipient primordia

46 The orientation of PIN1 within cells is shown by white arrows, and indicates auxin flow.

47 Auxin accumulates at I 1 position I1I1I1I1 Reprinted from Current Biology 15: Heisler, M.G., Ohno, C., Das, P., Sieber, P., Reddy, G.V., Long, J.A., and Meyerowitz, E.M. Patterns of auxin transport and gene expression during primordium development revealed by live imaging of the Arabidopsis inflorescence meristem, , Copyright (2005), with permission from Elsevier.

48 La polarità delle proteine PIN 1 determina un massimo di auxina in I1 I1I1I1I1

49 I1I1I1I1 This observation is consistent with the emergence of a primordium at the site of auxin application

50 dopo linizio della formazione del primordio la distribuzione di PIN1 cambia e orienta il flusso di auxina nel tessuto vascolare Poethig, R.S. and Sussex,I.M. (1985) The developmental morphology and growth dynamics of the tobacco leaf. Planta 165: Figure 3 Copyright (1985) Planta. Reprinted with kind permission of Springer Science+Business Media. Adapted by permission from Macmillan Publishers, Ltd: Nature Reinhardt D., Pesce, E.-R., Stieger, P., Mandel, T., Baltensperger, K., Bennett, M., Trass, J., Friml, J., Kuhlemeier, C. Regulation of phyllotaxis by polar auxin transport. Nature 426, ; copyright (2003). I1I1 P1P1 I1I1 P1P1 I1I1 P1P1 TIME

51 Una successiva inversione nella polarità di PIN1 cambia la posizione del picco di auxina e specifica la posizione del nuovo primordio P3P3 P2P2 P1P1 I1I1 P3P3 P2P2 P1P1 I1I1 I2I2 time

52 Summary Organ initiation at the shoot apical meristem is determined by auxin distribution and PIN1 An auxin maximum is necessary and sufficient to specify the site of primordium formation Primordia affect auxin distribution and so placement of incipient primordia Auxin has been proposed to act as a morphogen – a generator of form

53 Come viene acquisita lidentità di foglia?

54 The meristem is a population of small, undifferentiated, dividing cells. A leaf primordium is a population of small, undifferentiated, dividing cells.

55 The differ in their expression of critical regulatory genes; the meristem expresses meristem-specific genes, and the leaf primordium expresses primordium- specific genes.

56 Poethig, R.S. and Sussex,I.M. (1985) The developmental morphology and growth dynamics of the tobacco leaf. Planta 165: Figure 3 Copyright (1985) Planta. Reprinted with kind permission of Springer Science+Business Media. Ruolo dei fattori di trascrizione

57 KNOX-1 Geni di identità meristematica Class I KNOX genes (KNOX-1) (KNOX means Knotted-like homeobox) Expressed in meristem Not expressed in incipient primordia Help maintain indeterminate growth

58 Class I KNOX genes KNOX genes are Knotted-like homeobox genes that encode homeodomain transcription factors. Hao Yu, H., Yang, S.H., and Goh, C. J. (2000) DOH1, a class 1 knox gene, Is required for maintenance of the basic plant architecture and floral transition in orchid. Plant Cell 12:

59 Espressione di KNOTTED KNOTTED (a KNOX-1 gene) mRNA accumulates in the meristem but not the leaf primordia (arrows) of Zea mays. Jackson, D., Veit, B., and Hake, S. (1994) Expression of maize KNOTTED1 related homeobox genes in the shoot apical meristem predicts patterns of morphogenesis in the vegetative shoot. Development 120: 405–413. Reproduced with permission.Development 405–413.

60 STM un gene di classe KNOX1 è necessario per la formazione del meristema Reprinted by permission from Macmillan Publishers, Ltd: NATURE. Long, J.A., et al., 379: 66-69, copyright 1996.NATURE Wild-type plant showing leaf formation at the shoot apex The shootmeristemless mutant (stm) fails to form a shoot apical meristem during embryogenesis; notice the absence of leaf formation.

61 Geni Primordio-specifici ARP genes ARP is derived from three genes, ASYMMETRIC LEAF1, ROUGH SHEATH2, and PHANTASTICA ARP genes encode MYB transcription factors Expressed in cells of leaf primordia Promote determinate growth and differentiation ARP

62 Reprinted by permission from Macmillan Publishers, Ltd: NATURE. Byrne, M.E., et al., 408: Copyright NATURE ASYMMETRIC LEAF1 (AS1) mRNA is expressed in cotyledons but not in the meristem.

63 ARP Reprinted by permission from Macmillan Publishers, Ltd: NATURE. Byrne, M.E., et al., 408: Copyright NATURE In the stm mutant, AS1 is expressed in the meristem (arrow). Wild type stm mutant

64 Lespressione dei geni KNOX nel meristema reprime quella dei geni ARP ARP KNOX-1

65 Lespressione dei geni ARP reprime quella dei geni KNOX ARP KNOX-1

66 La sovraespressione di KNOX-1aumenta la complessità della foglia e la sua indeterminazione Chuck G et al., (1996) Plant Cell 8: Reprinted by permission from Macmillan Publishers, Ltd: NATURE GENETICS 31: 121 – 122. Hake, S., and Ori, N. Plant morphogenesis and KNOX genes. Copyright (2002). Arabidopsis Tobacco Maize WTOXWTOXWTOX

67 Mutazioni loss of funcion arp hanno fenotipo simile alla sovraespressione di KNOX-1 Reprinted by permission from Macmillan Publishers, Ltd: NATURE 408: Byrne, M.E., Barley, R., Curtis, M., Arroyo, J.M., Dunham, M., Hudson, A., and Martienssen, R.A. Asymmetric leaves1 mediates leaf patterning and stem cell function in Arabidopsis. Copyright (2000). Reproduced with permission Development Schneeberger, R., Tsiantis, M., Freeling, M., Langdale, J. Development (1998) 125: NATURE Development Wild-typeas1 WT as1 rs2 WT rs2 WT rs2 Arabidopsis Maize

68 Nei primordi i geni ARP agiscono come repressori trascrizionali dei geni di classe KNOX Guo, M., et al. (2008) Plant Cell 20:48-58 ARP heterodimer KNOX gene

69 Geni di confine (boundary) sono necessari per la separazione degli organi Boundary genes Ensure a sharp boundary between leaf and meristem Expressed at organ boundaries Loss-of-function leads to jagged or fused organs

70 GENI CUC

71 JLO expression JAGGED LATERAL ORGANS (JLO) is a boundary gene. Loss-of-JLO function causes fused or jagged organs. JLO coordinates KNOX-1 and PIN activities. Loss-of-function phenotype JAGGED LATERAL ORGAN (JLO) (LOBD gene family)

72 Summary A leaf acquires identity by turning OFF meristem genes and turning ON leaf genes KNOX-1, ARP and boundary genes encode transcriptional regulators that control expression of other genes Precise control of cell fates involves tight control of transcription by developmentally regulated activators and repressors

73 COME VIENE ACQUISITA LA POLARITA?

74 Polarità anatomica e funzionale Juarez, M. T., Twigg, R.W., and Timmermans, M.C.P. (2004) Development 131: Reproduced with permission.Development O2O2 CO 2 Most leaves have polarity – they are functionally and anatomically different on their upper and lower surfaces Abaxial surface - transpirational water loss, respiratory gas exchange Adaxial surface – light harvesting

75 Leaves have an inherent polarity because one side is more central and one more peripheral. Leaf Peripheral Central

76 Leaf Peripheral Central Adaxial Abaxial The central side is adaxial, and peripheral is abaxial. How does a leaf know which side is central?

77 The Sussex signal In the 1950s, Ian Sussex showed that a signal from the meristem is required for proper leaf polarity. Reprinted, with permission, from the Annual Review of Plant Physiology and Plant Molecular Biology, Volume 49 (c) 1998 by Annual Reviews

78 Incipient primordia were surgically isolated from the rest of the meristem by a small incision P3P3 P2P2 P1P1 I1I1 I2I2 I3I3 Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development

79 The isolated primordium lost polarity (it became entirely abaxialized) and became radially-symmetrical. P3 P2 P1 I1 I2 I3 P3P3 P2P2 P1P1 I1I1 I2I2 I3I3

80 Reinhardt, D., Frenz, M., Mandel, T., and Kuhlemeier, C. (2005) Development 132: Reproduced with permission.Development A more recent experiment showed that laser ablation of only the epidermal cell layer is sufficient for the primordium to lose its adaxial polarity.

81 A signal from the meristem moves through the epidermis into the incipient primordium. The signal conveys the adaxial positional information. The nature of the signal is not known.

82 Waites, R., and Hudson, A. (1995) Development 121: 2143 – Reproduced with permission.Development 2143 – 2154 The phantastica mutant of Antirrhinum (snapdragon) gives important clues to the basis of leaf polarity. Controllo genetico della polarità Wild-type phan

83 The phantastica mutant has radially symmetrical leaves. Waites, R., and Hudson, A. (1995) Development 121: 2143 – Reproduced with permission.Development 2143 – 2154 phan mutant leafWild-type leaf

84 Mutant phan leaves are abaxialized, indicating that PHAN is necessary for adaxial cell fate. phan mutant leafWild-type leaf

85 phan mutant leaf P3 P2 P1 I1 I2 I3 Surgical isolation The phan mutant leaves resemble the surgically isolated leaf primordia – Tutte le foglie radialmente simmetriche sono abaxializzate?

86 No: I mutanti Loss of function kanadi hanno foglie radiali adaxiali Eshed Y et al., Izhaki, A., Baum, S.F., Floyd, S.K., and Bowman, J.L. (2004) Development 131: Reproduced with permission.Development A triple mutant kanadi 1,2 and 3 has radial, adaxialized leaves KANADI genes promote abaxial cell fate

87 La perdita della identità adaxiale o abaxiale determina la radializzazione Wild type phan mutant kan mutant Eshed Y et al., Izhaki, A., Baum, S.F., Floyd, S.K., and Bowman, J.L. (2004) Development 131: Reproduced with permission.Development

88 Fenotipo del mutante Gain-of-function phb-1d Gain-of-function phb-1d mutants have radial, adaxialized leaves. McConnell, J.R. and Barton, M.K. (1998) Development 125: Reproduced with permission.Development

89 Cross section SEM In gain-of-function phb-1d mutants, PHB is expressed everywhere, resulting in adaxialized, radially symmetric leaves. Longitudinal sectionCross section In wild-type plants, PHB expression is restricted to the adaxial side of the leaves Reprinted by permission from Macmillan Publishers, Ltd: NATURE. McConnell, J.R., Emery, J., Eshed, Y., Bao, N., Bowman, J., and Barton, M.K. Nature 411: , copyright La mutazione The phb-1d mutation inluenza la distribuzione del mRNA di PHB

90 Reprinted by permission from Macmillan Publishers, Ltd: NATURE. McConnell, J.R., Emery, J., Eshed, Y., Bao, N., Bowman, J., and Barton, M.K. Nature 411: , copyright PHB promuove lidentità adaxiale Wild-type leaf: phb-1d leaf PHB expression = Adaxial No PHB expression = Abaxial

91 come PHB, PHV and REV promuovono lidentità adaxiale Like PHB, REVOLUTA (REV) and PHAVOLUTA (PHV) are expressed in the adaxial domain. Reprinted from Current Biology 13, Emery, J.F., et al., Radial patterning of Arabidopsis shoots by Class III HD-ZIP and KANADI genes, 1768–177, Copyright (2003), with permission from Elsevier.Current Biology

92 come PHB, PHV and REV promuovono lidentità adaxiale Loss of function triple phb / phv / rev mutant has radial, abaxialized leaves Reprinted from Current Biology 13, Emery, J.F., et al., Radial patterning of Arabidopsis shoots by Class III HD-ZIP and KANADI genes, 1768–177, Copyright (2003), with permission from Elsevier.Current Biology

93 La polarità richiede la corretta espressione di PHB Too much PHBToo little PHB Borghi, L., et al.,(2007) Plant Cell 19:

94 AAAAAAA AGO AAAAAAA miRNAs are short (~21-22 nt) RNAs that, in association with ARGONAUTE (AGO) target specific mRNAs for degradation (or interfere with translation). La espressione di PHB è regolata da miRNA

95 AAAAAAA In phb-1d plants, base changes in the PHB mRNA prevent miR166 from binding to it, allowing it to accumulate throughout the leaf primordium. x PHB-1D mRNA Reprinted by permission from Macmillan Publishers, Ltd: NATURE. Kidner, C.A. and Martienssen, R.A. Nature 428: 81-84, copyright 2004.; McConnell, J.R., Emery, J., Eshed, Y., Bao, N., Bowman, J., and Barton, M.K. Nature 411: , copyright AAAAAAA AGO In wild-type plants, miR166 binds to the PHB mRNA and degrades it on the abaxial side of the leaf primordium. miR166PHB mRNA Controllo della espressione di PHB da parte di miRNA

96 Additional support for role of miRNA in leaf polarity comes from the fact that the ago1 mutant has radial leaves; AGO is needed for miR166 function. ago mutantphb-1D mutant In ago mutants, as in phb-1D mutants, PHB mRNA accumulates throughout the leaf primordia. Reprinted by permission from Macmillan Publishers, Ltd: NATURE. Kidner, C.A. and Martienssen, R.A. Nature 428: 81-84, copyright 2004; McConnell, J.R., Emery, J., Eshed, Y., Bao, N., Bowman, J., and Barton, M.K. Nature 411: , copyright AAAAAAA AGO I miRNA controllano la polarità della foglia

97 These experiments demonstrate that in Arabidopsis miRNAs contribute to leaf polarity, by controlling the distribution of critical mRNAs. AAAAAAA AGO I miRNA contribuiscono alla determinazione della polarità della foglia

98 Cosa fanno tutti questi geni? KANADI 1,2,3 encode GARP transcription factors; YABBY genes have similar function and also encode putative transcription factors PHANTASTICA encodes a MYB transcription factor; PHB/ PHV/ REV genes encode HD-ZIP III transcription factors ADAXIALIZING GENES ABAXIALIZING GENES The genes regulated by these transcription factors are not yet known.

99 geni YABBY (FIL, YAB2, YAB3) promuovono il differenziamento del lato abaxiale delle foglie (SONO FATTORI DI TRASCRIZIONE ZINC –FINGER) Mutanti yab3 (omozigoti) producono foglie lobate che esprimono KNOX1 e formano meristemi ectopici e mostrano conversione abaxiale/adaxiale Il fenotipo yab suggerisce che ci sia incompatibilità tra la funzione KNOX e le funzioni che specificano lidentità ABAXIALE nella foglia

100 Modello per lacquisizione della polarità PHAN or PHB/PHV/REV miR166 KAN, YAB Adaxial fate Abaxial fate Meristem-derived signal

101 Il patterning ad/abaxiale può influenzare tratti agronomicamente importanti Wild-type rice leaf. Sclerenchymatous tissue forms on the abaxial surface and supports the leaf in an open form. Zhang, G-H. et al., (2009) Plant Cell 21:

102 SLL1 è una proteina GARP che influenza la polarità e larrotolamento della foglia sll1 mutant Wild-type In sll1 mutants, the supportive sclerenchymatous tissues on the abaxial surface do not form, causing the leaf to roll inwards. Zhang, G-H. et al., (2009) Plant Cell 21:

103 Rice plants with rolled leaves (like sll1) can have more erect leaves, reduced water loss by transpiration and higher yields. Wild-typesll1 mutant Zhang, G-H. et al., (2009) Plant Cell 21:

104 SUMMARY Leaves are initiated from cells in the shoot apical meristem Auxin gradients are important in leaf primordium initiation and positioning Leaf identity is determined by a change in expression of transcription-factor encoding genes Leaf polarity requires an unknown signal from the meristem and the domain-specific expression of adaxial- and abaxial- specific transcription factors

105 GENI DI IDENTITA ADAXIALE/ABAXIALE

106 mutazioni loss of function phan promuovono la conversione adaxiale/abaxiale (organi a simmetria radiale) I trascritti sono localizzati nel lato adaxiale Geni di identità adaxiale I mutanti phan hanno anche difetti nel mantenimento del meristema Interdipendenza destino adaxiale / meristematico PHANTASTICA (anthirrinum)/ AS1 (arabidopsis)

107 mutazione phan

108 Homeodomain leucin zipper proteins HD-ZIPIII contenenti un dominio START che lega lipidi PHABULOSA, PHAVOLUTA, REVOLUTA Fattori di trascrizione specifici per il lato adaxiale

109 PHB PHV REV Sono inizialmente espressi in maniera continua dal centro del SAM fino ai primordi fogliari; successivamente la loro espressione si restringe al lato adaxiale della foglia Mutazioni loss-of-function nei geni PHB o PHV o REV determinano conversione adaxiale/ abaxiale e incapacità di formazione o mantenimento del SAM Le funzioni PHB, PHV, REV sembrano positivamente correlate alla funzionalità dei geni KNOX Interdipendenza destino adaxiale / meristematico

110 La localizzazione nella regione adaxiale dei trascritti HD-ZIP III è regolata da: Geni KANADI (KAN ) espressi nella regione abaxiale (mutazioni recessive KAN determinano adaxializzazione e espressione ectopica di PHAV, PHAB, REV) microRNA ( mutazioni dominanti PHB e PHV inibiscono il riconoscimento e la degradazione dei trascritti genici ad opera di miRNA espressi specificamente nella regione abaxiale)

111 Regolazione da micro RNA dei geni HD-ZIP III Mutazioni in queste regioni danno luogo a fenotipi dominanti con foglie adaxializzate, radiali e meristemi più grandi miR165 miR166

112

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