Physiology of flowering plant Molecular level

1. Physiology of flowering plant Molecular level

2. Molecular studies on flowering crops Basic knowledge genes, gene expression profile control of gene expression Practical aspect e.g. breeding/improvement

3. Flowering At shoot apex Induction to InitiationtoSpecification VegetativetoReproductive IndeterminatetoDeterminate Shoot apical meristemto Inflorescence meristemto Floral meristem (primordia)

4. Flowering Signal Hormone Temperature Photoperiod Autonomous environment/endogenous

5. Floral stimulus production following inducing signal flowering switch to turn on florigen Site of flowering commitment shoot apex: require sufficient amount of floral stimulus for continuous flower production leaf: commit to continuously production of floral stimulus(irreversible)

6. Florigen: shoot apex or leaf Impatiens purple flower Short day for flowering 5 SD: flowering SD to LD: continue flowering SD toremove leavesto LD: leaves with purple petals

7. Florigen: shoot apex or leaf Impatiens red flower Short day for flowering 5 SD: flowering ReturntoLD: vegetative stage at inner whorls Require continuous supply of inducing signal

8. Flowering genes expressed in young leaf Maize: intermediate Arabidopsis: constans

9. Genes in Flower Development Structural gene Flower organ Flower color Flower scent Regulatory gene Protein product involved in controlling expression of other genes Via protein-DNA interaction

10. Flowering genes Timing Meristem identity Organ identity

11. Approaches Flowering mutant Gene identification Transformation Mutant complementation

12. Why flowering? Evolutionary diversificationof organisms Alteration of developmental events Variationin structure and regulation of genes controlling developmental mechanism

13. Why flowering? Flowers: invariant pattern and organization Perianth/Reproductive organs Varied number, size and position

14. Flowering genes Study model: Arabidopsis and Snapdragon Common characteristics: Floral-specific expression with different roles Identified as homeotic genes Control specification of meristem and organ identity of flower

15. Flowering genes 2 classes: meristem identity genes eg, LFY CAL AP1 organ identity genes eg, AP2 AP3 PI AG Most genes encode proteins with homologous regions of ~ 260 amino acid sequence similarity: common ancestor

16. Flowering genes Highly conserved regionabout 57 amino acid called MADS box also found in yeast and human Regulatory gene family: transcription factor MADS box gene in other crops: tomato tobacco potato petunia

17. Homeotic gene: identity of organs/body parts pattern and position Sequence-specificDNA-bindingmoiety: animal: homeodomain (homeobox gene) plant leaf: homeodomain protein floral organ: MADS box protein / gene

18. Meristem identity genes Meristem: SAM (indeterminate) for shoot IM (indeterminate) for inflorescence FM (determinate)for flower

19. Meristem identity genes Inflorescence meristem Mutant: early flowering in Arabidopsis Conversion of IMto FM Terminal flower tfl TFL protein Negative regulatorof LFY and AP genes

20. Meristem identity genes Floral meristem Mutant: partial conversion of FM to IM Leafy in Arabidopsis Floricaula in Snapdragon LFY and FLO protein Positive regulatorof AF3 and PI genes

21. Meristem identity genes Floral meristem Mutant: indeterminate flower within flower (sepal, petal, petal etc) Agamous (AG) in Arabidopsis Plena (PLE) in Snapdragon Protein: putative transcription factor

22. Meristem maintenance genes Meristem: - small, dense, large nuclei - to supply new cells - undifferentiated cells (central) - daughter cells with specific developmental fates (subdistal)

23. Meristem maintenance genes Mutant: no meristem (strong allele) Reduced number of meristematic cells No effect of root meristem Shoot meristemless, stm stm-5 mutant: 1-2 leaves then terminate leaf primordia consume central zone

24. Meristem maintenance genes STM protein: Produced throughout development Maintain shoot and floral meristem Inhibit differentiation in central zone Activate cell division/proliferation

25. Floral Initiation Process (FLIP) Arabidopsis structural development - rosette leaves with compact internode - elongated internode with cauline leaves and lateral inflorescence (bolting) - nodes without leaves and flowers

26. Floral Initiation Process (FLIP) Transition from early to lateinflorescence Loss of indeterminate growth Inhibit inflorescence program Inhibit leaf, lateral shoot development Initiate specific floral organ Activate perianth development Inhibit reproductive organ development

27. FLIP genes TFL LFY AP1 AP2 TFL: timing of phase transition Tfl mutant: correct sequence of development early bolting early flowering reduced number of inflorescence internode

28. LFY/AP1/AP2: required in combination rapid and complete transition Mutant: gradual transition from inflo. to flower flower-like lateral shoot leaf in first whorl reproductive organs in outer whorls etc. Late in flower development ReduceFLIPgenes, increasegametegenes

29. Floral Organ Identity Organs with appropriate identity for their positions ABCmodel 3 classes of genes: A, B and C workingindividual and in pair A and C inhibit/antagonize each other (no simultaneous functions)

30. 1 2 3 4 B A C A sepals whorl 1 A+Bpetals whorl 2 B+Cstamens whorl 3 C carpel and determinacy whorl 4

31. ABC model: Developed from floral homeotic mutants of Arabidopsis and Antirrhinum (flowers with abnormal organ pattern) Genes identified: MADS-box family (transcription factor with conserved domain) Also work well in petunia, tomato and maize

32. A mutant abnormal in whorl = abnormal in organ = B mutant abnormal in whorl = abnormal in organ = C mutant abnormal in whorl = abnormal in organ =

33. AP1, SQUA Mutant sepaltoleaves and no petal Class = AP2 Mutant sepalstoleaves or carpels petalstostamens Class=

34. AP3, DEF Mutant petalsto sepalsand stamensto carpels Class= AG, PLE Mutant stamenstopetalsandcarpelstosepals Class=

35. A-class mutantwith different phenotypes Varied from predicted pattern Some floral homeotic genes (MADS box) not follow ABC model: newE-class control 3 inner whorls and determinacy ABC modelnecessary but not sufficient **D-class for ovule identity**

36. E-class or Identity mediating factors Imgenes:MADS boxgenes Transcription factor arabidopsis SEP petunia FBP2 tomato TM5 Mutants: changes in organ identity in 3 inner whorls loss ofdeterminacy

37. Arabidopsistriplemutant (sep1 sep2 sep3) 4 sepals 4 sepals 6 sepals new mutant flower petunia FBP2: functional equivalent toSEP protein (complementation ofsepmutant) E-classessential for function ofB and C class

38. Revised ABC model B Im/E class A and C Other factors sepal petal stamen carpel

39. Quartet model of floral organ identity interaction between MADS-domain proteins to form DNA bindingdimers B-classprotein form dimer with each other or withA-classprotein C-classprotein withE-classprotein ternaryorquaternarycomplex B- andC-classprotein with A-classandE-classprotein

40. Floral organ identity controlled by 4 different combinations of 4 floral homeotic proteins e.g. Arabidopsis whorl 1: A-class AP1 homodimer whorl 2: A-class AP1, B-class AP3 and PI, E-class SEP whorl 3: B-class AP3 and PI, C-class AG, E-class SEP whorl 4: C-class AG, E-class SEP heterodimer

41. Blooming gene When to flower winter spring summer too early: no pollinating insect too late: not enough time to make seed (winter) one gene: CONSTANSin Arabidopsis control flowering time CONSTANS protein helps measure day length

42. Quality of light perceived by 2 light receptors cryptochrome 2 responds to blue light phytochrome A responds to red light CONSTANS protein: amount above threshold Light receptors: activated Sunlight: late afternoon time for flowering **hundreds of genes involved to build flower**

43. Color and Color pattern Flower color: important for pollination Different perception of color red flower – visible to hummingbird -- colorless to bee Changes in petal color : effect on pollinator type Color pattern: differential accumulation of pigment

44. Color and Color pattern Flower color: Accumulation of flavonoids Major pigments: anthocyanins orange, red and purple Vacuole: site of anthocyanin accumulation Transport as glutathione conjugate

45. Flower Color Anthocyanin synthesis pathway Biosynthesis enzymes/genes identified

46. Flower Color Anthocyanin synthesis pathway regulation at transcriptional level Different colors: different enzyme activities or substrate/precursor availability in different steps Mutations: accumulation of intermediates new color

47. Flower Color Factors on flower perception co-pigmentation vacuolar pH cell shape

48. Flower Color Co-pigmentation anthocyanin and flavonols / flavones shift in absorption spectrum differential gene expression: different enzyme activities changes in pigment ratio

49. Flower Color Vacuolar pH pH increase  blueing seven loci (ph1-ph7) control pH in petunia mutation of the ph loci effect on pH in petal extract but not on anthocyanin composition regulatory genes?

50. Flower Color Cell shape effect on optical properties conical shape: higher light absorption appear velvet sheen flat shape: faint color