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Origins of Multicellularity

Origins of Multicellularity. Chlamydomonas Gonium Pandorina Eudorina Pleodorina Volvox. Structural Progressions in Colonial Green Algae. “The Volvocine Lineage”. Alternation of Generations. Evolutionary Emphasis on the Diploid Soma.

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Origins of Multicellularity

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  1. Origins of Multicellularity Chlamydomonas Gonium Pandorina Eudorina Pleodorina Volvox Structural Progressions in Colonial Green Algae “The Volvocine Lineage”

  2. Alternation of Generations Evolutionary Emphasis on the Diploid Soma Diploid (2n) Phase Haploid (n) Phase mitosis sori 2n Fertilization Meiosis Ferns mitosis 2n n n Mosses

  3. Arabidopsis thalianaThe Thale or Mouse-Eared Cress

  4. The Arabidopsis Life Cycle Embryo (2n) Ovule (n) Pollen (n) flowering rosette growth

  5. Nuclear Genome 5 chromosomes 125Mb (10x yeast) 14% transposable elements25,500 genes (4.5x yeast) 11,000 gene families +79 (chloroplast) +58 (mitochondrion)

  6. COGs in the Genomics Wheel ca 2000

  7. Transformation by Agrobacteriumthe Crown Gall Bacterium

  8. imbibition, vernalization -> radicle outgrowth Germination Shoot apex hypocotyl elongation (note apical hook) Photomorphogenesis (hook opening, cotyledon greening) Root hairs Root apex

  9. Photomorphogenesis Cryptochromes and Phytochromes

  10. Three Primary Tissues • Dermal • Epidermis • Ground • General Tissue • Vascular • Xylem • Phloem Enhancer trap GUS construct

  11. Topless-1 embryos make an apical root Plant Embryogenesis

  12. Shaping the Plant Cell Cellulose Synthase Microtubules Overlay Complexes

  13. Meristems

  14. Tunica Organization of Shoot Meristems L3 Radial Zones Layers L1/L2/L3 chimeras

  15. Embryo/Seedling Mutants Apical-basal mutations (b-e) Radial symmetry mutations (f,g) Organogenesis mutations (h-j)

  16. Axial Mutants

  17. Cross section of root Root Structure

  18. Root Hairs video microtubules

  19. Epidermal Fates gl1 ttg No Leaf Hairs But Lots of Roots! WT

  20. WT has 8 files of root hairs GL2::GUS expressed in N cells Root Hair Specification ( )

  21. The Flowering Stimulus Day length and Temperature leaf phloem apex FL-C FL-T Florigen is the protein encoded by the FL-T locus; it is produced in the leaves and moves through the plant to the meristems to transmits the flowering response through the plant

  22. stigma, carpels Conversion to a Floral Meristem • Vegetative meristem • Floral meristem identity genes • (Lfy, Ap1, Cal; Tfl) • Floral meristem • Mapping genes (define boundaries) (Su) • Floral organ identity (homeotic) genes (whorl identity) • Sepals (Ap2) • Petals (Ap2, Ap3, Pi) • Stamens (Ap3, Pi, Ag) • Carpels (Ag)

  23. The ABC Model of Floral Whorl Identity B (Ap3, Pi) A (Ap2) C (Ag) Sepals Petals Stamens Carpels ag ap2 pi

  24. A Few Questions for Thought • Explain the evolutionary origins of multicellular organisms. What are the benefits and costs of multicellularity? • Compare and contrast plant and animal (drawing upon your own general knowledge) body plans. • Describe how a new plant is formed during development (from fertilization through germination). • What are meristems, and why are they important in plant biology? • What are the three primary tissues of the plant body? • What is the difference between a shoot and a root meristem? Between a vegetative and a floral meristem? • How are organ identities in determined in the flower? What are the role(s) of homeotic genes in this process?

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