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Flowers and seeds

Flowers and seeds

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Flowers and seeds

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  1. Flowers and seeds

  2. The plant kingdom • ~ 275,000 flowering plants! • Focus on angiosperms • Brief foray into gymnosperms and ferns • Apologies to the rest of the kingdom for lack of coverage Tegeder and Ward, 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355764/

  3. Alternation of generations The gametophytic (n) and sporophytic (2n) generations Gametophyte haploid Sporophyte diploid or polyploid

  4. Alternation of generations The sporophytic generation may be diploid (2n = 2x) or polyploid (2n = _x) 2 pairs of homologous chromosomes 2 sets of homoeologous chromosomes AABB 3 pairs of homologous chromosomes 3 sets of homoeologous chromosomes AABBDD 1 pair homologous chromosomes. 1 pair of the 7 pairs of chromosomes. The V locus and 2 possible alleles at the locus • A A B B • A A B B D D V V VAVAVBVB VAVAVBVBVDVD 2n = 6x = 42 90,000 genes 2n = 2x = 14 ~30,000 genes 2n = 4x = 28 60,000 genes

  5. Sexual reproduction in Angiosperms Advantages > disadvantages

  6. Angiosperms Polyploidy: frequent VAVA VAVAVBVB VAVAVBVBVDVD 2n = 6x = 42 90,000 genes 2n = 2x = 14 ~30,000 genes 2n = 4x = 28 60,000 genes

  7. Reproductive organs and gamete formationDevelopment of the female gametophyte • Reproductive structure: Ovule(s), style, stigma http://www.extension.org/pages/32204/stigma

  8. Development of the female gametophyte arizonabeetlesbugsbirdsandmore.blogspot.com Pollinator attraction: Nectar, Color, Aroma “Nectar contains water, sugars and amino acids to attract pollinators and defenders and is protected from nectar robbers and microorganisms by secondary compounds and antimicrobial proteins…More research is needed to understand how plants produce nectar, the most important mediator of their interactions with mutualistic animals.” Heil. 2011. https://www.cell.com/trends/plant-science/fulltext/S1360-1385(11)00006-9

  9. Development of the female gametophyte • Pollinator attraction: Petunia species and pollinators. • Key roles for Myb transcription factors genes; ~ 200 different ones! Hummingbird-pollinated P. exserta Bee-pollinated P. integrifolia Hawkmoth-pollinated P. axillaris • ANTHOCYANIN2 (AN2) • Activates anthocyanin biosynthesis • Functional • Nonsense mutations • ODORANT1 (ODO1) • Regulates methylbenzoate volatile • + 10X volatile production • Baseline volatile production Yuan et al. 2013. https://www.sciencedirect.com/science/article/pii/S1369526613000654?via%3Dihub

  10. Development of the female gametophyte Disseminator attraction Blue rose Tulipomania Transgenic: + Delphinidin from pansy; - knock-down of 2 endogenous rose genes http://www.suntoryapplause.com/ Virus infection Lesnaw and Ghabrial. 2000. https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS.2000.84.10.1052

  11. Development of the female gametophyte • Megaspore mother cell (MMC)  • MMC undergoes meiosis • Of 4 megaspores produced 1 survives (most species) • Three post-meiotic mitoses http://botit.botany.wisc.edu/Resources/Botany/Angiosperms/Lilium%20Life%20Cycle/Ovulate/Megaspore%20mother%20cell.jpg.html 1 2 3

  12. Development of the female gametophyte • The 8-nucleate embryo sac (1 egg, 2 synergids, 2 primary endosperm nuclei, 3 antipodals) Source: yougems.reflectionsinfos.com lima.ohio-state.edu

  13. Development of the male gametophyte • Reproductive structures: Anthers; pollen within anthers

  14. Development of the male gametophyte • Pollen mother cell (PMC)  • Meiosis gives a tetrad of microspores • https://www.researchgate.net/figure/10-Microspore-mother-cell-stage-3-Section-of-a-single-locule-showing-early-microspore_fig3_12698228 Note, this is different than ♀ Meiosis 1 Meiosis 2

  15. Development of the male gametophyte • The first mitosis gives vegetative and generative nuclei; at the second mitotic division, the generative nucleus gives 2 sperms. mitosis mitosis mitosis mitosis mitosis mitosis mitosis mitosis

  16. The pollen pathway • The stigma is the site of pollen recognition • Pollen germinates and the vegetative (tube nucleus) grows through the style to the ovule • The two sperm use the tube as conduit

  17. The pollen pathway • Corn silks and pollen https://ipm.missouri.edu/IPCM/2012/7/Corn-Pollination-the-Good-the-Bad-and-the-Ugly-Pt-3/

  18. Double fertilization • One sperm fertilizes the egg to give the 2n embryo, the other fertilizes the polar nuclei to give the 3n endosperm antipodals ♀ ♀ 3n endosperm polar nuclei ♂ ♀ ♀ ♀ ♂ ♀ egg 2n embryo synergids

  19. Double fertilization in angiosperms: The Movie A review… N N n n N N n n n nn n n n nn MMC Nn OR MMC Nn n n N N n n N N N NN N N N NN N n PMC Nn Nn sporophytic generation N N n n n N N n N n N N n n

  20. After double fertilization…. • ….there are at least four independent and genetically distinct generations coexisting in the angiosperm seed: • maternal sporophyte diploid tissue • maternal gametophyte haploid tissue • offspring sporophyte diploid tissue • fusion of male (1) and female (2) gametophyte to form triploid tissue

  21. The gymnosperms • ~ 1,000 species Tegeder and Ward, 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355764/

  22. Sexual reproduction in Gymnosperms • Advantages > disadvantages https://landscapeplants.oregonstate.edu/plants/pseudotsuga-menziesii

  23. Gymnosperms: • Alternation of generations: 2n n • Polyploidy: rare • Sequoia sempervirens – only known hexaploid (2n = 6x = 66) https://landscapeplants.oregonstate.edu/plants/sequoia-sempervirens

  24. Gymnosperms Gamete formationDevelopment of the male and female gametophyte • Male and female cones can also be • At different position on same tree • On separate trees

  25. Gymnosperms • The female gametophyte: • After meiosis, 1 of 4 megaspores (each of them n) becomes the egg • 3 of 4 megaspores have structural functions or degenerate • Slow growth (~ 1 year) • The male gametophyte: • After meiosis, 4 microspores • Usually wind dispersal of pollen • Slow growth of pollen tube (~1 year) • 2 sperm: one fertilizes egg, other degenerates

  26. Gymnosperms • No double fertilization • No ovary • The seed • ~ 2 years to mature • Nutritive tissues are haploid megagametophte (female) • diploid embryo • seed coat (diploid female sporophyte)

  27. The ferns and horsetails • ~ 13,000 • No seeds, no flowers • Spores! Tegeder and Ward, 2012. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355764/

  28. Sexual reproduction in ferns and horsetails Advantages > disadvantages https://www.fs.fed.us/wildflowers/beauty/ferns/index.shtml

  29. Ferns and horsetails • Alternation of generations: 2n and n are free-living: 2n n • Polyploidy: common http://www.alabamaplants.com/Ferns/Ophioglossum_crotalophoroides_page.html

  30. Ferns and horsetails Gametes: formation and fertilization https://www.quora.com/Where-would-you-find-a-fern-gametophyte https://www.luc.edu/biology/111lab/algae-seedless-plant/photos/ferngametophyte40x/

  31. Cool fern links • USFS • American Fern Society • Ferns - the secret life • Ferns - the movie The comeback of the horsetails https://oregonstate.edu/dept/nursery- weeds/weedspeciespage/horsetail/Equisetum_arvense_horsetail.html https://www.bendbulletin.com/lifestyle/5887191-151/horsetails-have-been-around-since-before-dinosaurs

  32. Seeds

  33. Seeds https://www.atlasobscura.com/places/judean-date-palm-methuselah http://www.pnas.org/content/104/35/14169

  34. Seeds - looking ahead to Mendelian genetics N N N n N N n + = N N N n n n N N N n n n n n n n + = n n n n n n n n n N N N N N N N + = N N N N N N N N N n n N n n n N = + n n n N N N n n n Note: At this point in the figure, were are focusing on an Angiosperm, the antipodals and synergids are deleted and only the fertilized endosperm nuclei (now 3n) and fertilized egg (now 2n) are shown. Only the fertilized egg is carried to the Punnett square.

  35. Embryo genetics the focus, but remember the 3n endosperm (angiosperms) Berner and Hoff. 1986. 26:876-878

  36. Embryo genetics the focus, but remember xenia “Because the endosperm is the bulk of what we see and eat when we consume sweet corn, sweet corn breeders must work with an unusual genetic effect called xenia. Xenia refers to observable effects that occur due to the influence of pollen. In sweet corn, the two most important traits affected by pollen are kernel color and sweetness. For example, yellow kernel color is dominant to white, and if a white variety receives pollen from a yellow variety, yellow kernels will appear among the white ones.” https://ofrf.org/sites/ofrf.org/files/How_to_Breed_Organic_Sweet_Corn.pdf

  37. Embryo genetics the focus, but remember megagametophyte (gymnosperms) http://www.vcbio.science.ru.nl/en/virtuallessons/gymnosperma/

  38. Seeds and persistence https://timeline.com/methuselah-judean-date-palm-b3782ff1d731 https://www.feedipedia.org/node/687