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Computational Systems Biology Flower development

Computational Systems Biology Flower development. Teemu Teeri 23.2. 2006. Flower development in four parts. ABC and beyond Induction of flowering Meristems and prepatterns Regulatory networks. Part 1 ABC and beyond Homeotic genes that determine organ identity in flowers. Arabidopsis.

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Computational Systems Biology Flower development

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  1. Computational Systems Biology Flower development Teemu Teeri 23.2. 2006 Flower development

  2. Flower development in four parts • ABC and beyond • Induction of flowering • Meristems and prepatterns • Regulatory networks Flower development

  3. Part 1ABC and beyondHomeotic genes that determine organ identity in flowers Flower development

  4. Arabidopsis Stamen Petal Sepal Carpel Flower development

  5. Homeotic mutants Homeosis: ‘Something has been changed into the likeness of something else’ Bateson 1894 Wilhelm Johannsen William Bateson Flower development

  6. Homeotic mutants Flower development

  7. Homeotic mutants grow correct organs in wrong places Normal flower A mutant B mutant C mutant Flower development

  8. B A C petal sepal stamen carpel ABC model for organ identity determination in flowers Flower development

  9. ABC model for organ identity determination in flowers Flower development

  10. B C carpel stamen stamen carpel B A C A B A C petal sepal stamen petal petal carpel sepal sepal carpel sepal carpel sepal The ABC model explains homeotic mutants in flowers Flower development

  11. B C carpel stamen stamen carpel B A C A B A C petal sepal stamen petal petal carpel sepal sepal carpel sepal carpel sepal Mutant phenotypes in Arabidopsis Flower development

  12. C carpel carpel carpel carpel A sepal sepal sepal sepal Double mutantsin Arabidopsis A- B- B- C- Flower development

  13. A- B- C- B C A C carpel carpel carpel carpel leaf leaf leaf leaf A sepal sepal sepal sepal Double mutantsin Arabidopsis A- B- B- C- Flower development

  14. ABC genes in Arabidopsis and snapdragon Flower development

  15. MADS I C K N MADS I K C N 56 aa, highly conserved, DNA-binding, dimerisation 27-42 aa, considerable sequence variability 70 aa, moderately conserved, keratin related, protein-protein interactions Poor or no sequence conservation A region present in AG and related MADS proteins MADS domain family of transcription factors Flower development

  16. Expression domains of ABC MADS-box genes correlate with their function AGAMOUS APETALA3 Flower development

  17. transcription M2 M2 M1 M1 MADS domain proteins bind DNA as dimers g e n e Flower development

  18. globosa deficiens DEF DEF DEF GLO GLO GLO The two B-function genes form an autoregulatory loop GLO DEF Flower development

  19. A- B- C- B A C leaf leaf leaf leaf ABC MADS-box genes are necessary for development of flower organs Are they sufficient? No, expression of ABC genes in leaves does not convert leaves into flower organs. Flower development

  20. carpel anther petal sepal B A C petal sepal carpel anther Phylogeny Among the ABC MADS-box genes, phylogenetic position and genetic function correlate. Flower development

  21. Arabidopsis MADS-box genes AGL2, AGL4 and AGL9 group outside of the ABC genes in fylogeny. When mutated, there is no change in flower phenotype. Flower development

  22. In a triple mutant for AGL2, AGL4 and AGL9, all organs in the Arabidopsis flower develop into sepals W1 W2 W3 W4 Triple mutant Wild type Organs W1-W4 Flower development

  23. AGL2, AGL4 and AGL9 were renamed to SEPALLATA1, SEPALLATA2 and SEPALLATA3 W1 W2 W3 W4 Triple mutant Wild type Organs W1-W4 Flower development

  24. B- C- A sepal sepal sepal sepal The triple mutant resembles the double mutant where B and C function genes are inactive The SEPALLATA function (SEP1, SEP2 or SEP3) is needed to fulfill both the B function and the C function in Arabidospis. Flower development

  25. Quaternary complexes of MADS domain proteins Flower development

  26. The Quartet Model of flower development Flower development

  27. A- B- C- B A C leaf leaf leaf leaf ABC and SEP MADS-box genes are necessary for development of flower organs Are they sufficient? Flower development

  28. Conversion of Arabidopsis leaves into petals Rosette leaves Cotyledons Flower development

  29. Scanning electron microscopy is used to define organ identity Flower development

  30. B A C petal sepal stamen carpel Unifying principles of flower development • ABC model • Striking in its simplicity • Applicable to a wide range of flowering plants • Central role of LEAFY • Necessary and sufficient to specify a meristem as floral • Integrator of floral induction pathways • Key activator of the ABC genes Flower development

  31. Part 2How do we get there?Induction of flowering Flower development

  32. CO FLC AGL20 AGL24 LFY/FLO Meristems and phase transitions Vegetative meristem Inflorescence meristem Flower meristem wt Flower development

  33. Multiple inductive pathways control the timing of flowering • Long-day photoperiod • Gibberellins (GA) • Vernalization • Autonomous pathway Flower development

  34. Induction of flowering Multiple cues Flower development

  35. Induction of flowering Multiple cues Multiple cues are integrated by FLC, SOC1, FT and LFY Flower development

  36. Meristem identity genes • Shoot meristem identity genes • TERMINAL FLOWER 1 (TFL1) • Floral meristem identity genes • LEAFY (LFY) • APETALA 1 (AP1) Flower development

  37. SnapdragonTFL1 –> CEN, LFY –> FLO Inflorescence meristem Flower meristem CEN FLO cen FLO centroradialis mutant wild type Flower development

  38. TFL1 TFL1 LEAFY LFY Meristem identity genes Vegetative meristem Inflorescence meristem Flower meristem wt Flower development

  39. 35S-TFL1 35S-LFY 35S-AP1 LFY ↓ AP1 ↓ TFL1 ↓ TFL1 versus LFY and AP1 Flower development

  40. Part 3Meristems and prepatternsHow ABC is laid down? Flower development

  41. Meristems are stem cells of the plant Flower development

  42. CLA3 CLAVATA3 expression is dependent on WUSCHEL  Stable feedback loop that maintains the size of SAM WUS Maintenance of the shoot apical meristem SAM SAM CLA3 WUS WUS expression gives the meristem a prepattern Flower development

  43. Other prepatterns UFO UFO UNUSUAL FLOWER ORGANS (UFO) patterns all meristems Flower development

  44. Other prepatterns Floral SAM Vegetative SAM LEAFY LEAFY marks the flower meristem Flower development

  45. A wus mutant flower: central organs are missing WUS induces AGAG represses WUS SAM AG WUS Flower development

  46. A wus mutant flower: central organs are missing WUS induces AGAG represses WUS SAM AG WUS + LEAFY Unlike CLAVATA3, AGAMOUS expression is only initially dependent on WUSCHEL Flower development

  47. WUS induces AGAG represses WUS SAM AG LEAFY Repression of the SAM organizer terminates the meristem Unlike CLAVATA3, AGAMOUS expression is only initially dependent on WUSCHEL Flower development

  48. WUS induces AGAG represses WUS SAM ag WUS + LEAFY Failure in repression of the SAM organizer keeps the meristem proliferating Flower development

  49. AP1 is initially expressed throughout the meristem SAM AP1 LEAFY APETALA1 is induced by LEAFY Flower development

  50. B A C AG represses AP1 SAM AG AP1 LEAFY Flower development

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