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- Today’s Lecture - Trichome development And Switching into reproductive phase

- Today’s Lecture - Trichome development And Switching into reproductive phase. For more info--. Szymanski DB, Lloyd AM, Marks MD. Progress in the molecular genetic analysis of trichome initiation and morphogenesis in Arabidopsis. Trends Plant Sci. 2000 May;5(5):214-9. Review.

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- Today’s Lecture - Trichome development And Switching into reproductive phase

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  1. - Today’s Lecture -Trichome developmentAnd Switching into reproductive phase BMB/BIOL/ENT 430

  2. For more info-- • Szymanski DB, Lloyd AM, Marks MD.Progress in the molecular genetic analysis of trichome initiation and morphogenesis in Arabidopsis. Trends Plant Sci. 2000 May;5(5):214-9. Review. • Michaels, S. D. and R. M. Amasino. 2000. Memories of winter: vernalization and the competence to flower. Plant Cell & Environment23: 1145 -1154. See-- http://www.biochem.wisc.edu/amasino/publications.html BMB/BIOL/ENT 430

  3. Plant Trichomes-- insight into cellular differentiation in plants • Trichome = hair like structure that extend from the epidermis of aerial tissues • Function of trichomes-- boundary layer between epidermis and environment • Reduce heat and water loss • Protection against herbivory and pathogens • Secretion of chemicals or physically limit access BMB/BIOL/ENT 430

  4. Trichome on Lemon Basil Capitate trichome from Ocimum ssp. (Lemon Basil) http://fisher.bio.umb.edu/pages/JFTrich/trichome.htm 2001 BMB/BIOL/ENT 430

  5. Plumbago-- trichomes protecting nectories http://www.botany.hawaii.edu/faculty/webb/BOT201/Angiosperm/plumbago.htm BMB/BIOL/ENT 430

  6. Example-- Arabidopsis trichomes Fully formed & Developing Developing BMB/BIOL/ENT 430

  7. Arabidopsis Trichome • An Arabidopsis trichome is a single cell • Trichomes can be branched • The basal portion is called the stalk • There are three spikes in the apical portion. BMB/BIOL/ENT 430

  8. Trichome Number and Distribution • Normal plants have leaves with evenly spaced solitary trichomes • The Try mutation causes formation of small clusters of 2-5 trichomes; therefore the normal TRY gene regulates the number of trichomes at any specific position BMB/BIOL/ENT 430

  9. Trichome development-- • Steps in development • Cell proliferation-- number of cells per trichome • Differentiation • Inter-cellular communication-- lateral inhibition to get regular spacing • Morphogenesis control-- branching • Control in development • Integration with leaf development (cell division and expansion) • Hormone levels • Vegetative phase development BMB/BIOL/ENT 430

  10. Restricted Cell Division in Trichome development • A normal trichome has endoreduplication (DNA replication) but no mitosis and cytokinesis, • THEREFORE-- cell division is inhibited • The SIAMESE (SIM) gene is required for this inhibition • In sim mutants, trichome cell continue to divide, resulting in multi-celled trichomes BMB/BIOL/ENT 430

  11. Morphology versus Cell Division • Because plant cells don’t move, cell division is thought to be critical for plant morphogenesis • In the sim mutant, trichomes are multi-cellular, but they have normal morphology • This is indicates that alteration of cell division does not automatically change morphology BMB/BIOL/ENT 430

  12. GL1 TTG1 GL3 CPC GL1 TRY TTG1 TRICHOME INITIATION Genetic Regulation of Trichome Initiation • Series of checks and balances • Initiation • Glabrous1 (GL1) • Transparent Testa Glabra1 (TTG1) • Glabrous3 (GL3) • Checks • Glabrous1 (GL1) • Transparent Testa Glabra1 (TTG1) • Triptychon (TRY) • Caprice (CPC) BMB/BIOL/ENT 430

  13. GL1 and TTG proteins • GL1 encodes a MYB-domain protein; • MYB domain proteins are probably transcription factors • TTG encodes a WD-40 domain protein; • WD-40 domain can interact with other proteins • GL1 and TTG proteins regulate the expression of genes needed for trichome initiation and endoreduplication • Evidence suggests these form a protein complex that controls trichome initiation BMB/BIOL/ENT 430

  14. TRICHOME INITIATION TRY GL2 GL3 DNA synthesis in absence of cell division (polyploid) Morphogenesis Genetic Regulation of Trichome Formation • Endoreduplication-- synthesis of DNA w/o cell division • Glabrous2 (GL2) • Inhibit by Triptychon (TRY) • Morphogenesis (aerial expansion of cell and spacing) • Glabrous3 (GL3) • Glabrous2 (GL2) BMB/BIOL/ENT 430

  15. Genes Regulating Early Cell Growth • GL2 is needed for the local outgrowth, and encodes a homeodomain protein • Many genes regulate the extension growth and morphogenesis. • Mutants in these genes have abnormally-shaped trichomes BMB/BIOL/ENT 430

  16. Cytoskeleton and Morphology • Actin filament is a major component of cytoskeleton • Actin filament form thick cables during trichome growth and disruption of actin filament causes distorted growth • Actin filament organization is abnormal in trichome growth mutants: alien, crooked, dis1, gnarled, klunker, and wurm BMB/BIOL/ENT 430

  17. Genes involved in branching • Several genes control the branching to trichomes • Evidence indicates that they interact with cytoskeleton and microtubule formation • Zwichel -- kinesin-like motor protein • Furca gene family, Angustifolia and stachel BMB/BIOL/ENT 430

  18. Pathways in trichome development BMB/BIOL/ENT 430

  19. - Meristems - What controls the type of structures meristems generate? • Vegetative growth verses Reproductive growth (inflorescence and flowers) • Shift in plant development is a change in fate of meristem Vegetative Inflorescence flowers • Timing of switch is regulated by environmental factors (light, temperature, gravity, moisture and nutrients) BMB/BIOL/ENT 430

  20. Meristem identity Vegetative versusInflorescence? Shoot meristem formation and maintenance [Review article] Michael Lenhard, Thomas Laux Current Opinion in Plant Biology 1999, 2:44-50. BMB/BIOL/ENT 430

  21. Regulation of vegetative to reproductive transition • Internal vs. external factors • Signals may vary among plants BMB/BIOL/ENT 430

  22. When to flower? That is the question. • Variation among plants in triggers to flower (annual / biennial / perennial) • Three independent pathways: • Long-day pathway (photoperiod) • Autonomous Pathway • Vernalization (cold-treatment or extended exposure to cold) • Gibberrellin (GA) BMB/BIOL/ENT 430

  23. Photoperiod or daylength controls switch from vegetative growth to reproductive growth is From floral induction to floral shape [Review article] Detlef Weigel. Current Opinion in Plant Biology 1998, 1:55-59. BMB/BIOL/ENT 430

  24. Light Perception-- Red and Far Red Light • Plants have several types of light receptors • One type is called phytochrome, which can absorb red and far red light • In Arabidopsis, there are five isoforms of phytochromes: • PhyA, PhyB, PhyC, PhyD, and PhyE BMB/BIOL/ENT 430

  25. Phytochromes • Phytochromes have two domains: • A light-sensing domain • A protein kinase domain • Light (photon) probably causes a change of conformation in the light sensing domain, which activates the protein kinase domain BMB/BIOL/ENT 430

  26. Photoperiod-- • Controls Constans (Co) gene • Affects downstream genes controlling the meristem. • Meristem identity genes -- Master regulatory genes of floral initiation • Induction of inflorescence • Leafy (LFY) • Terminal flower (termination of meristem) BMB/BIOL/ENT 430

  27. Autonomous Pathway • Flowering is inhibited by Flowering locus C (FLC) • Autonomous-pathway genes (FCA, FLD, LD and FVE) promote flowering by down-regulating FLC. • In biennial plants, FRI (Frigida) up-regulates FLC leading to delayed flowering (i.e. vegetative growth is prolonged). • FRI is dominant over the effects of the autonomous pathway genes. BMB/BIOL/ENT 430

  28. Autonomous Pathway • Balance between vegetative and flowering phases, depends upon FLC expression in annual plants Low FLC, Flower on! Mutant LD, Flower off! BMB/BIOL/ENT 430 Richard M. Amasino, 2001 http://www.biochem.wisc.edu/amasino/

  29. -- Vernalization --Cold treatment triggers flowering by downregulating FLC expression Flower on! Flower off! Richard M. Amasino, 2001 http://www.biochem.wisc.edu/amasino/ BMB/BIOL/ENT 430

  30. Interaction of pathways to flowering-- as determined by genetic experiments Reeves PH, Coupland G.Analysis of flowering time control in Arabidopsis by comparison of double and triple mutants. Plant Physiol. 2001 Jul;126(3):1085-91 BMB/BIOL/ENT 430

  31. Floral initiation -- genetic regulation • Meristem identity genes -- Master regulatory genes of floral initiation • Induction of inflorescence • Leafy (LFY) • Unusual floral organs (UFO) • Apetala1 (AP1) • Cauliflower (CAL) • Apetala2 (AP2) • Maintenance of flowering - • Terminal flower • Agamous BMB/BIOL/ENT 430

  32. Master regulatory genes of floral initiation • Induction of inflorescence-- switch from vegetative to inflorescence • Primary genes-- initial role in floral fate • Leafy and Apetala1-- major roles, • LOF -- no floral structures • GOF -- precocious flowers form • Gene regulation -- transcriptional activators • Leafy expressed first, turns on Apetala1 and Cauliflower-- Feedback on each other BMB/BIOL/ENT 430

  33. gof lof Genetic control of shoot and flower meristem behavior [Review article] Sarah J Liljegren, Martin F Yanofsky. Current Opinion in Cell Biology 1996, 8:865-869. Floral meristem Identity Genes -- induction of inflorescence BMB/BIOL/ENT 430

  34. Master regulatory genes of floral initiation • Maintenance of flowering - • How many flowers to form? • How to stop making additional flowers within a flower? BMB/BIOL/ENT 430

  35. Maintenance of flowering • Two genes of opposite actions • Terminal flower -- keeps meristem active forming additional floral meristems (stalk of flowers)-- • LOF, one flower • Agamous -- terminate cell division and additional generation of floral program within a floral meristem • LOF-- flower within a flower, etc. BMB/BIOL/ENT 430

  36. Floral Meristem ID genes -- LOF phenotypes The making of a flower: control of floral meristem identity in Arabidopsis [Review] Pidkowich, Klenz and Haughn. Trends in Plant Science, 1999, 4:2:64-70 BMB/BIOL/ENT 430

  37. Next lecture-- How to make a flower? (Please read Chapter 20 before this lecture) BMB/BIOL/ENT 430

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