Flowers and seeds

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/

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

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

Sexual reproduction in Angiosperms Advantages > disadvantages

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

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

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

Development of the female gametophyte Pollinator attraction: Petunia species and pollinators. Key roles for Myb transcription factors genes; ~ 200 different ones! Bee-pollinated P. integrifolia Hummingbird-pollinated P. exserta 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

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

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

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

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

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

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

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

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/

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

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

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

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

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

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

Gymnosperms Gamete formation Development of the male and female gametophyte Male and female cones can also be At different position on same tree On separate trees

Gymnosperms No double fertilization No ovary The female gametophyte: 4 megaspores (n,n,n,n) produced; 1 (n) forms functional megaspore. Slow growth (~ 15 months). The male gametophyte: ~ 4 (n) cells/pollen grain Pollen dispersal: usually wind-pollinated (pollen found in mid-Atlantic!) Pollen tube (n) ; slow growth (~15 months!) 2 sperm (n,n): one fertilizes egg, other degenerates The seed: ~ 2 years to mature. Nutritive tissues are haploid megagametophte (female); diploid embryo; seed coat (diploid female)

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

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)

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

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

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

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/

The comeback of the horsetails 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

Seeds

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

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 NN Nn nn + = 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.

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

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

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

Seeds and persistence https://www.chabad.org/library/article_cdo/aid/588226/jewish/Masada.htm https://www.feedipedia.org/node/687