Plant Reproduction Strategies

Human Manipulation of Plants

• Modern humans used to be hunters and gatherers
• Humans moved to agriculture and plant dependence 9000 years ago
• Early plant cultivation involved unconsciously selecting for certain characteristics
• Biotechnology allows the production of genetically modified organisms (GMOs)

Artificial vs. Natural Selection

• Flowering plants reproduce sexually which provides variability for selection
• Variability is achieved through the shuffling of genes and mutations that cause changes to DNA sequences
• Natural selection favors the fittest individuals based on offspring production
• Artificial selection occurs when humans select desirable traits.

Natural Selection Conditions

• Natural selection is a process that occurs if a population has variation among individuals, consistent relationship between a trait and fitness differences, and heritability for the trait between parents and offspring
• The process will result in a change in the frequency of the trait

Artificial Selection vs. Natural Selection in Angiosperms

• Selection changes the genetic makeup either by man's choice or change in genetic makeup caused by biotic and abiotic factors
• The major force of evolution in animals is nature versus humans selected plants
• Humans selected for: high yields, value, appearance, and pest resistance.
• Changes in gene frequencies are impacted by these biotic (living agents, competition, coronavirus, disease) and abiotic (non-living agents: soil type, altitude, rain, wind) factors

Traditional Methods of Plant Manipulation

• Enhancement of inbreeding
• Asexual propagation of plants

Inbreeding vs. Outcrossing

• With inbreeding, flowering plants are bisexual, pollen transferred within a flower itself, or between similar plants
• Fusion of gametes within a flower (perfect) takes place or fusion happens between genetically similar plants (imperfect)
• Inbreeding provides high yields of seeds but low variability and is common in annual herbs and weeds

Self-Compatibility in Inbreeding

• Inbreeding occurs if a flower is self-compatible
• Two key factors for this self-compatibility are the close proximity inside the plant and for the stamen and pistil mature at the same time

Outcrossing

• Outcrossing is the fusion of gametes between genetically different individuals and leads to genetic diversity
• It is advantageous when environmental conditions change
• Strategies used by angiosperms to achieve outcrossing include: temporal separation, spatial separation, and genetic incompatibility which is the most common.

Temporal Separation

• The timing of the flower facilitates outcrossing, with the male and female flower parts developing at different times

Selection for Self-Pollination

• Humans select mutations that facilitate self-pollination

Genetic Incompatibility

• Genetic incompatibility ensures outcrossing by preventing inbreeding by not allowing pollen to be as effective on the same plant

Farmer Inbreeding Preference

• Farmers prefer inbreeding because it results in a reproduction of homozygous individuals and are genetically identical meaning they are stands of even plants in terms of quality
• There is also decreased need to plant together and there is a single parent
• Seeds produced from genetically identical parents are of even quality
• Inbred lines produce uniform seeds

Asexual Reproduction

• Asexual reproduction clones are not genetically unique
• In seeds are produced from undifferentiated cells.
• There is reduced variability amongst plants and vulnerability to fungal attacks.
• Vegetative propagation uses pieces of leaves or stems for plant clones, and they grow and mature faster and are also less vulnerable to fungal attacks
• These methods ensure crop uniformity, even more than inbreeding

Grafting

• Grafting is an artificial method of asexual reproduction
• With the scion, it carries the desirable character ex. fruit size and flavor
• With the rootstock, it's several eyars old and cold tolerant
• Splice involves joining a scion to a rootstock for propagation
• Grafting on a bud is used to reproduce a specific plant variety; success involves seeing the scission
• Cleft grafting joins stem pieces together at the root, done when there are few buds available

Grafting Advantages

• Grafting can produce more harvest
• It saves a lot of space, you can have 3 varieties on 1 rootstock
• It can attract different pollinators
• The scion and rootstock should belong to the same family

Speciation: Plant Evolution

• Allopatric speciation: a population geographically splits in two, the two populations evolve differences leading to speciation, and population a becomes different than population b
• Sympatric speciation: instantaneous speciation, but due to polyploidy, can occur by chance alone or induced by chemicals
• Sympatric speciation is the main reason behind evolution in domesticated plants
• Allopatric speciation occurs in different geo conditions

Polyploidy

• Polyploidy is more than two sets of chromosomes (triploid, tetraploid, hexaploids, etc)
• This leads to large plants, fruit, and seeds.

Autopolyploidy

• Autopolyploidy relates to a plant species that generally have smooth leaves has undergone a mutation and some leaves are hairy

Two Types of Polyploidy

• Allopolyploid: polyploid of hybrid sets from two two different species
• Autopolyploid: individual with more than two sets from the same species

Example of Allopolyploidy

• Triticale is a human-made cereal allopolyploid
• Triticale = Wheat (4n=28) X Rye (2n=14)
• Wheat gives high yield, rye gives hardiness

Autopolyploidy Meiotic Error

• Autopolyploidy occurs when an individual derived from one species has more tahn 2 sets of derived chromosome from the same species, due to meiotic error

Autopolyploidy Applications

• Treating a plant with colchicine results in autopolyploidy, resulting in plants with larger flowers/fruit

Early Experiments in Altering Plant Genes

• A new allele can be introduced to the plant by natural mutation
• Agronomists in the 20th century used mutagens = X rays/chemicals to induce mutations in sex cells -- all trials failed to obtain useful cultivars

Agronomist Dream

• Have plants produce their own nontoxic pesticides
• Have plant resistance to herbicides
• Maturation without a mushy flesh
• Production of medicine for humans

Beyond Traditional Methods: Biotechnology

• Biotechnology uses living organisms to provide products for humanity
• Two techniques include protoplast manipulation and genetic engineering

Protoplast Manipulation

• An early gene tech technique has been protoplast manipulation
• The process involves adding enzymes to dissolve plant cell walls into protoplasts
• Cells are assayed for a desired trait, ex. herbicide resistance
• Fusion of 2 proplasts is done by PEG, a hybrid is produced, and grown on proper media
• Cells are grown until the tissue forms a Callus which can allow a propagator
• You end with a new hybrid plant

Genetic/Generic Engineering (GMO)

• Species may not the have certain traits and need genes inserted
• Major crops are asexual and do not involve traditional breeding
• Insect repellent genes are required
• Plasmids acts as a bacterial carrier and are often used for genetic engineering

Ti-Plasmid

• Agrobacterium tumefaciens cell acts as a vector
• The Ti-plasmid induces tumors and crown gall disease
• Promotors initiate the gene, where a marker indicates it's presence
• Transgenic plant in the lab made from insertion with ballistic method

Biotechnology Products in 1990

• Important uses have become biopharming
• Producing human serum albumin
• Producing tobacco plant for insulin
• Potato producing antibodies
• Plants resistant to herbicides such as glyophosate
• BT crops = plants producing nontoxic insecticide
• Plants resistant to frost

Explore the nuances of plant reproduction, from the disadvantages of inbreeding to the advantages of outcrossing. Understand temporal separation, human selection for self-pollination, and the implications of agamospermy. Learn key concepts in angiosperm reproductive strategies.