plant breeding systems diversity and evolution of reproduction in angiosperms
TRANSCRIPT
PLANT BREEDING SYSTEMS
Diversity and Evolution of Reproduction in Angiosperms
Plants vs. Animals
Plants vs. Animals
• Flowering plants are generally hermaphroditic.
Plants vs. Animals
• Flowering plants are generally hermaphroditic.
• Use intermediary agents.
Plants vs. Animals
• Flowering plants are generally hermaphroditic.
• Use intermediary agents.
• Can reproduce asexually & sexually.
Plants vs. Animals
• Flowering plants are generally hermaphroditic.
• Use intermediary agents.• Can reproduce asexually
& sexually.
• Less rigidly controlled development– meristematic tissue
everywhere.
Asexual Reproduction
• Reproduction of genetically identical individuals from a single parent plant.– Via cloning or agamospermy
• No meiosis, no fertilization, and no recombination.
Advantages of Asexual Reproduction
• Parent plants well-adapted to local environment will have offspring with a competitive advantage.
Advantages of Asexual Reproduction
• Parent plants well-adapted to local environment will have offspring with a competitive advantage.
• Colonization with limited dispersal.
Modes of Vegetative Reproduction
Modes of Vegetative Reproduction
• Rhizomes– underground shoots
• Tillers– aboveground shoots
• Bulblets– “little bulbs”
• Bulbils– inflorescence veg buds
• Cuttings
Agamospermy/Apomixis
• “Seeds w/o gametes”– Production of seeds genetically identical to
parents asexually, w/o fertilization
• ~40 families, 130 genera, 400 species
• Obligative or facultative• May have evolved independently multiple
times from sexual ancestors.
Modes of Agamospermy
• Embryo sac develops w/o meiosis w/ unreduced 2n egg cell & develops into zygote.
Modes of Agamospermy
• Embryo sac develops w/o meiosis w/ unreduced 2n egg cell & develops into zygote.
• Embryo sac aborts and a veg cell from surrounding sporophytic tissue (ovary wall) develops into zygote.– Rubus, Taraxacum officinale
Sexual Reproduction
• Production of offspring through meiosis and fertilization of egg by sperm (post-pollination).– Offspring genetically different from parents due
to recombination.
• Plants can be both asexual and sexual, with a variety of forms.
Hermaphroditic Flowers
• Self-compatible (SC)– Capable of self-fertilization
or cross-fertilization
• Self-incompatible (SI)– Only capable of cross-
fertilization
– Inability of hermaphroditic plant to produce zygotes w/ self pollen
Autogamy
• Self-fertilization
• Pollen transfer within or among flowers of same individual
• ~25% of plant taxa
Advantages of Autogamy
Advantages of Autogamy
• Insures seed set in absence of pollinators.
Advantages of Autogamy
• Insures seed set in absence of pollinators.
• Overcomes sterility.
Advantages of Autogamy
• Insures seed set in absence of pollinators.
• Overcomes sterility.
• Selectively advantageous by transmitting both sets of genes to offspring.– Well-adapted genotypes preserved.
Advantages of Autogamy
• Insures seed set in absence of pollinators.
• Overcomes sterility.
• Selectively advantageous by transmitting both sets of genes to offspring.– Well-adapted genotypes preserved.
• Only single colonizing individual needed.
Disadvantages of Autogamy
Disadvantages of Autogamy
• Decreases genetic variability.
Disadvantages of Autogamy
• Decreases genetic variability.
• Inability to adapt to changing conditions.
Disadvantages of Autogamy
• Decreases genetic variability.
• Inability to adapt to changing conditions.
• Increases inbreeding depression.– Reduces heterozygosity and increases
homozygosity of deleterious alleles.– More uniform populations.
Cleistogamy (CL)
• Flowers never open and only capable of self-fertilization in bud.
• Inconspicuous, bud-like apetalous flowers that form directly into seed capsules.
• Has evolved independently multiple times– throughout the angiosperms,
including some basal lineages.
• 488 species, across 212 genera and 49 families.– Violaceae, Fabaceae, Poaceae
Cleistogamy (CL)
• Mixed mating systems -can produce both CL and CH on an individual.
• CL fls are a “back-up” in case pollinators scarce.
• CL occur after normal flowering period. – CH fls early spring and CL fls
rest of season.
• CL fls occur through mutations with loss of SI.
Self-incompatibility (SI)
• Involves a biochemical rxn in the stigma/style to reject self pollen and prevent pollen tube growth.
• Genetically controlled by S-locus– opposite S alleles attract– like S alleles repel
Sporophytic SI
• Diploid genotype of sporophyte parent determines what matings will be successful.
• Interaction between pollen exine and stigma/style tissues.
• Pollen will not germinate on stigma of flower that contains either of 2 alleles in sporophyte parent that produced pollen.
Gametophytic SI
• Haploid genotype of pollen grain (gametophyte) determines what matings will be successful.
• Interaction between pollen tube and stigma/style tissues.
• Pollen grain will grow in any pistil that does not contain the same allele.
• 50% of angiosperms
Advantages of Self-Incompatibility
Advantages of Self-Incompatibility
• Prevents selfing and expression of deleterious genes that are heterozygous in parents.
Advantages of Self-Incompatibility
• Prevents selfing and expression of deleterious genes that are heterozygous in parents.
• Reduces inbreeding depression.
Advantages of Self-Incompatibility
• Prevents selfing and expression of deleterious genes that are heterozygous in parents.
• Reduces inbreeding depression.
• Increases genetic exchange/diversity.
Advantages of Self-Incompatibility
• Prevents selfing and expression of deleterious genes that are heterozygous in parents.
• Reduces inbreeding depression.
• Increases genetic exchange/diversity.
• Ability to adapt to changing conditions.
Disadvantages of Self-Incompatibility
Disadvantages of Self-Incompatibility
• Relies on effective cross-pollination, seed dispersal and establishment.
Selfers vs. Outcrossers
• SC• Small flowers (few)• Unscented flowers• Nectaries & nectar guides
absent• Maturation of
reproductive parts– Anthers near stigma– Style included
• All fruits mature• Low pollen/ovule ratio
• SI or SC• Large showy flowers (many)• Scented flowers• Nectaries & nectar guides
present• Differential maturation of
reproductive parts– Anthers far from stigma– Stigma well-exserted
• Only some fruits mature• High pollen/ovule ratio
Strategies to Prevent Self-fertilization
Physical Separation of Reproductive Parts (Herkogamy)
• Within flowers • Among flowers
Heterostyly
• Flowers in different individuals of the same species having 2 or 3 different style lengths– With stamen lengths varying inversely
• Distyly• Tristyly
Distyly
• 2 floral morphs.
• “Thrum” flower – long filaments w/ short styles
• “Pin” flower– short filaments w/ long styles
• Only pollinations between different floral morphs are successful.
• E.g.: Primula
Tristyly
• 3 floral morphs• Style long, stamens
short and medium• Style medium,
stamens short and long• Style short, stamens
medium and long
Physical Separation of Reproductive Parts
• Unisexual flowers– Staminate and
carpellate flowers
• Monoecy
• Dioecy
Monoecy
• Common in wind-pollinated plants.
• Common in temperate regions.
• Self-pollination possible but less likely.
Dioecy
• 4% of angiosperms– Scattered throughout
• Common in tropical regions and oceanic islands
• Gen small fl size• 100% outcrossing, but
inefficient• Often controlled by sex
chromosomes– Silene
Polygamous Flowers
• Both bisexual and unisexual fls on the same plant.
– Androdioecy = bisexual and staminate individuals in a population.
– Andromonoecy = bisexual and staminate flowers on same individual.• Euphorbia, Solanum
– Gynodioecy = bisexual and carpellate individuals in a population.• Sidalcea hendersonii, Silene
– Gynomonoecy = bisexual and carpellate flowers on same individual.• Silene, Solidago
– Polygamodioecy = some plants with bisexual and staminate flowers & some plants with bisexual and carpellate flowers in a population.
– Polygamomonoecy = bisexual, staminate, and carpellate flowers on same individual.
Evolution of Dioecy• From hermaphroditism
– Vestigial sex organs– Few families entirely dioecious
• From monoecy• From SC
– W/in groups that have lost original GSI system
• From distyly– Unequal pollen flow & gender
function– Change in pollinator frequency– Non-functional anthers at low level
in female flowers– Non-functional pistil in male flowers
Temporal Separation of Reproductive Parts(Dichogamy)
Temporal Separation of Reproductive Parts(Dichogamy)
• Protandry– Anthers release pollen
before stigma receptive
– Common in insect-pollinated plants
• Geranium maculatum– 1st day flower
– 2nd day flower
Temporal Separation of Reproductive Parts(Dichogamy)
• Protogyny– Stigma receptive
before pollen release
– Less common than protandry
• Magnolia grandiflora– 1st day flower
– 2nd day flower
Geitonogamy
• Self pollination between different flowers on same plant.
Evolution of Breeding Systems
• Evolutionary trends go both ways and in a variety of ways.
Evolution of Breeding Systems
• Evolutionary trends go both ways and in a variety of ways.
• Ancestral angiosperms were SC, hermaphroditic.
Evolution of Breeding Systems
• Evolutionary trends go both ways and in a variety of ways.
• Ancestral angiosperms were SC, hermaphroditic.• SI has evolved many times.
– SC has evolved from SI plants as well.
Evolution of Breeding Systems
• Evolutionary trends go both ways and in a variety of ways.
• Ancestral angiosperms were SC, hermaphroditic.• SI has evolved many times.
– SC has evolved from SI plants as well.
• Physical and temporal separation have evolved many times.
Evolution of Breeding Systems
• Evolutionary trends go both ways and in a variety of ways.
• Ancestral angiosperms were SC, hermaphroditic.• SI has evolved many times.
– SC has evolved from SI plants as well.
• Physical and temporal separation have evolved many times.
• Dioecy has evolved many times.
Evolution of Breeding Systems
• Evolutionary trends go both ways and in a variety of ways.
• Ancestral angiosperms were SC, hermaphroditic.• SI has evolved many times.
– SC has evolved from SI plants as well.
• Physical and temporal separation have evolved many times.
• Dioecy has evolved many times.• Breeding systems not fixed, but labile.