Flowering, reproduction and Terminator technology

Plant Physiol Biotech 3470

Lecture 14

Thurs 15 March 2006

Salisbury and Ross, “Plant physiology” 4th edn

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

gymnosperms

angiosperms

Rost et al., “Plant biology”, 2nd edn

• 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

Rost et al., “Plant biology”, 2nd edn

Most terrestrial plant species are angiosperms

• 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

Most angiosperm species produce bisexual, or perfect flowers

♀ ♂

– Monoecious• Stamens and pistils on different

parts of the same plant• Maize, cucurbits, oaks

– Dioecious• Male and female flowers on different

plants!• Spinach, Cannabis, holly, Ginkgo

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)

Scientific American, August 2004

This technique is widely used for both traditional and molecular breeding for crop improvement

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– Bananas desperately need new disease resistance alleles– Potatoes are susceptible to fungal infection (e.g., by

Phytopthera)• 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 thisAsk: 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

Copycontrol.org

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

Coding region

Transcription start

Consider the benefits of seeds that cannot sprout

• The frequency of outcrossing of transgenes to wild populations of related plants would decline – No viable seeds would be left behind in the field that

could crossbreed with wild relatives

• 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?