Flowering, reproduction and Terminator technology Plant Physiol Biotech 3470

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Flowering, reproduction and Terminator technology

  • Plant Physiol Biotech 3470

  • Lecture 14

  • Thurs 15 March 2006

Angiosperms and gymnosperms are the two major groups of land plants

  • Vascular plants (a/k/a “higher” plants) include

    • Ferns and relatives
    • Cycads and rare gymnosperms
    • Conifers (common gymnosperms)
    • Flowering plants (angiosperms)
      • Monocotyledons (monocots; grasses)
      • Dicotyledons (dicots)
  • Angiosperms and gymnosperms both reproduce through the production of seeds and pollen

    • They are seed plants

Most terrestrial plant species are angiosperms

  • Angiosperms and gymnosperms differ by the location of their female plant parts (ovules, which contain the eggs)

  • In gymnosperms these are often located inside cones on modified leaves (bracts)

  • Angiosperms by definition have ovules borne inside fleshy structures called ovaries

  • Ovaries are flower parts; flowers are unique to angiosperms

  • Angiosperms dominate the earth’s vegetation

  • Almost all crop plants, orchard trees, garden plants and ornamentals are flowering plants

Most angiosperm species produce bisexual, or perfect flowers

  • Angiosperm flowers can be perfect or imperfect

  • Perfect flowers are bisexual and have both male (stamens) and female (pistils or carpels) parts

    • This includes the vast majority of flowering plants
    • We are familiar with many of them!
    • Wheat, rice, potatoes
  • Imperfect flowers have either stamens or pistils but not both

  • Imperfect flowers can be further subclassified

What do perfect and imperfect flowers have to do with farming and plant reproduction?

  • The type of flowers produced by a crop species influences how it is grown

    • This is because crop products are (almost) all seeds (fruits) !
  • Perfect flowers often reproduce by self-pollination [a/k/a selfing] (pollen that fertilizes the ovule comes from the same flower or plant)

  • This means that the alleles in the selfed seed will be the same as in the parent plant

    • There are usually 2 alleles available to heterozygotes (A and a)
    • However different phenotypes may result depending on whether the offspring possess the dominant (AA or Aa) or recessive (aa) alleles
  • Saving seed from perfect flowers is thus possible and will not affect next generation yield and seed quality

Breeding is the control of pollen flow in crop plants to produce a desired offspring

  • Ensuring that different pollen pollinates female flower parts can be done by removing male sexual organs (anthers) before the pollen is mature

  • This is what Mendel did when he crossed pea plants

  • For imperfect flowers, crossing between plants can be controlled in the field and greenhouse by covering female plant parts and dusting them with pollen of choice

  • e.g., for a monoecious species like maize, place glassine envelopes over maize silks (female flowers)

Let’s get to the Source article

  • It states that “agrochemical” companies like Monsanto can tell farmers which seeds to plant (T or F?)

  • It specifically alleges that these companies are targeting small scale farmers who only grow what they eat (subsistence farming)

  • It also states that large plant biotech companies are acquiring other seed companies (for their g_____ stocks) at a rapid rate to improve their seed (T or F?)

  • It also alleges that genetically modified food is potentially harmful to humans (T or F?)

The truth…

  • Subsistence farming is not particularly “noble” or “natural” as implied in the article

  • It is practiced by the poorest people in the world

  • It consists of intense labor for meager yields

  • Farmers do not want to work hard for nothing

  • They would love to plant higher yielding seed varieties

  • The real problem preventing them from doing this is poverty:

    • They cannot afford inputs to maximize yield
      • Seed
      • Chemicals / fertilizer
      • Fuel
      • Irrigation
  • Their saved seed likely represents local varieties selected to do best under an uncontrolled growing environment

Heritage crop plant varieties are living gene banks

  • Important observation:

  • These seeds are potentially sources of new alleles allowing plants to grow well under biotic and abiotic stress

  • This is especially important given the single varieties of crop plants that dominate markets

  • Preserving heritage varieties is thus very important!

  • Seed banks perform this role for many crops (tomatoes, wheat, corn, etc.)

  • New breeding should always be performed to genetically diversify major crop plants and be ready for pathogens that might wipe out a crop

Replanting monoecious plants dilutes their desirable combination of allelles

  • No farmer can be “forced or coerced by a corporation or their government to grow patented seed”

    • They are small businessmen!
    • They can buy whatever seed they like
  • For monoecious plants like maize, the yield increase seed in hybrids means that the parentage of these plants is very important

    • Remember that specific combinations of inbred parents give heterozygotic offspring that are much bigger (a/k/a h_________ )
  • We have seen that planting selfed monoecious seed is undesirable agronomically for farmers because it increases the effort for harvest and reduces yield

Terminator technology is copy protection for seeds

  • This technology makes seed unable to regrow

  • In these seeds, embryos may germinate but do not survive

  • There are many ways to do this

  • Ask: what genes are important for permitting embryos to grow?

  • These are potential targets for preventing germination

    • Genes for proteins that mobilize stored photoassimilate (e.g., starch hydrolyzing enzyme in endosperm a/k/a a______ )
    • Genes for structural proteins important for shoot and root growth
    • Genes for proteins of photosynthesis and energy metabolism
  • Expression of these genes can be shut down in embryos by several methods

Terminating embryo growth requires careful control of gene expression

  • Key question: Is the gene whose expression you wish to shut down only expressed in the embryo?

  • A thorough understanding of metabolism is required prior to interfering with the expression of a gene

  • e.g., you do not want to prevent starch hydrolysis everywhere in the plant: where is it important?

  • Targeting shutting down the gene properly in time and place requires selection of the right elements within genes that control their expression

    • These are part of the gene upstream from the coding sequence and are called p_______s

Consider the benefits of seeds that cannot sprout

  • The frequency of outcrossing of transgenes to wild populations of related plants would decline

  • Seeds could be stored for longer periods of time without affecting their physiology and chemical makeup

    • An advantage for farmers and food processors
  • Patent protection for seed companies

    • Each trait costs millions of dollars to get to market

Any “unnatural” change to crop plants is greeted skeptically

  • The article appeals to passion without explaining why it is a good idea to ban Terminator technology

  • No elaboration is made on the “growing body of evidence” that GM food has harmful effects in animals that consume it

    • This is highly dependent on the transgene
    • Different plants can modify proteins in novel ways that can precipitate immune responses in humans
    • Each transgenic trait must be tested for its effects on humans and animals consuming it

Some last thoughts…

  • Monsanto actually stopped developing Terminator technology in the late 1990s

  • It was poorly named for mass acceptance

  • Our group at Monsanto Protein Technologies had some ideas for introducing this trait into our corn plants expressing antibodies (protein drugs against cancer)

  • We still think about these even now!

  • Can you think of any other ways to shut down a genome?

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