1. Gene transfer, asexual reproduction, sexual reproduction, and apomixis
Plant Reproduction
 Gene transfer, asexual reproduction, sexual reproduction, and apomixis
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2. Asexual reproduction The clone is immortal
Example: Allium sativum
“As far as we know, garlic in cultivation throughout history has only been propagated asexually by way of vegetative cloves, bulbs, and bulbils (or topsets), not from seed. These asexually propagated, genetically distinct selections of garlic we cultivate are more generally called "clones". Yet this asexual lifestyle of cultivated garlic forgoes the possibility of combining traits proffered by interpollinating diverse parental stocks.”
Source:

3. Asexual reproduction The clone is immortal
Example: Populus tremuloides
The world's heaviest living thing
1 clone in the Wasatch Mountains of Utah
47,000 stems of genetically identical aspen trees
Total weight: 6 million kilograms
Aspen is dioecious species - this clone is one big male
source:

4. Sexual reproduction Advantages > disadvantages
Genetic variation:
Allele exchange via cross-pollination
New combinations of alleles via meiosis
Purge deleterious mutations
Stay ahead in the host-pathogen “arms race”
Potential adaptation to a changing climate

5. Sexual reproduction Advantages > disadvantages
In a dioecious species, half the reproductive effort is wasted in producing males
Meiosis produces some "unfit" combinations of alleles
Cross-pollinated plants may be subject to environmental conditions unfavorable to pollination
Finding a mate

6. Alternation of generations
In plants there is an alternation of the gametophytic (n) and sporophytic (2n) generations
(Gametophytic = haploid)

7. Alternation of generations
The sporophytic generation may be diploid (2n = 2x) or polyploid (2n = _x)
VAVA
VAVAVBVB
VAVAVBVBVDVD
2n = 2x = 14
30,000 genes
2n = 4x = 28
60,000 genes
2n = 6x = 42
90,000 genes
1 pair homologous chromosomes
0 sets of homoeologous chromosomes AA
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
A A B B D D

8. Angiosperm reproductive organs and gamete formation Development of the female gametophyte
Reproductive structure: Ovule(s), style, stigma

9. Angiosperm reproductive organs and gamete formation Development of the female gametophyte
Megaspore mother cell (MMC) 
MMC undergoes meiosis
Of 4 megaspores produced 1 survives (most species)
Three post-meiotic mitoses 1 2 3

10. Angiosperm reproductive organs and gamete formation 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

11. Angiosperm reproductive organs and gamete formation Development of the female gametophyte
Pollinator attraction: Petals, nectaries, etc.
Source: arizonabeetlesbugsbirdsandmore.blogspot.com

12. Angiosperm reproductive organs and gamete formation Development of the male gametophyte
Reproductive structures: Anthers; pollen within anthers

13. Angiosperm reproductive organs and gamete formation Development of the male gametophyte
Pollen mother cell (PMC) 
PMC undergoes meiosis
Meiosis gives a tetrad of microspores
Note, this is different than ♀
Meiosis 1
Meiosis 2

14. Angiosperm reproductive organs and gamete formation 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

15. The pollen pathway and double fertilization
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

16. The pollen pathway and double fertilization
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

17. The pollen pathway and double fertilization
After double fertilization, there are at least four independent and genetically distinct generations coexisting in the 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

18. A review… V v sporophytic generation v v V V V v v V V V V V V V V V
MMC
V v V V
v v v V V
v v v v
v v v v v
PMC
V v v V
V v
sporophytic
generation
v v
V V v V v V v V
v v
V V

19. A review of sexual reproduction in an F1 plant, heterozygous for the Vv locus+ = v
v v
V V V
V V
V V v
V v + = V
V V
V V V
V V V v VV Vv vv + = V
V V
v v v
v v
v v V
v V + = v
v v
v v v
Note: At this point in the figure, 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.

20. Seeds without sex: Apomixis
Apomixis involves parthenogenesis – development of an egg without fertilization, as opposed to parthenocarpy – development of fruits (seedless) without fertilization
Implication - Apomixis allows for seed propagation of a heterozygote – genetically identical from generation to generation.
Obligate:  
Facultative: 

21. Seeds without sex: Apomixis
Hand and Koltunow Genetics 197:

22. Seeds without sex: Apomixis
Economic implications of apomixis
Why would apomixis be, or not be, of commercial interest to purveyors of hybrid seeds? 
If transgenic apomicts are developed and released, and if apomixis is dominant, it will be necessary to control pollen flow – if not, there will be frozen gene pools
Evolutionary implications of apomixis
Obligate vs. facultative

23. Seeds without sex: Apomixis
Prevalence 400 species ; 40 families; Common in Poaceae, Asteraceae, Rosaceae
Examples
Tripsacum
Poa pratensis
Pennisetum
Dandelion (Taraxacum spp)
Rubus

24. Seeds without sex: Apomixis
How it works
no (or altered) meiosis to produce unreduced female gametophyte (embryo sac)
no fertilization – but do get autonomous embryo formation
may have autonomous endosperm development, or endosperm development may be triggered by fertilization. Most cases it is triggered by fertilization (pseudogamy = fertilization of central cell)  

25. Seeds without sex: Apomixis
Genetic basis
Apomixis loci and candidate genes
Lots of breeding effort; little success
Epigenetically regulated?

26. The Rubus armeniacus case study Himalayan (Armenian) blackberry

27. Is the Himalayan blackberry the perfect weed?
Designing the perfect invasive
Attribute
Description
Flower
Hermaphroditic
Pollination biology
Self and outcross
Apomixis
Facultative
Seeds
Small and numerous
Vegetative propagation
Yes
Ploidy level
Polyploid
Protection
Thorns
Attraction
Tasty fruit
Was Luther Burbank the “father” of this perfect weed?
promo.idahopotato.com