Biology Answering 4 questions

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Genetically Modified Foods ST4

Learning Objectives

ST 4.1 What Are GM Foods?

ST 4.2 Methods Used to Create GM Plants

ST 4.3 GM Foods Controversies

ST 4.4 The Future of GM Foods

ST 4.1 What are GM Foods?

Defining Genetically Modified Foods

• Genetically modified foods (GMOs): Derived from genetically modified organisms

– Genetically modified organisms: Plants and animals of agricultural importance whose genomes have been altered

– Modified via genetic engineering or recombinant DNA technologies

Why make GM foods?

• Address malnutrition – increase yield of food – More than 200 different GM foods have been

created – Example: Golden Rice: A variety of rice that

contains the vitamin A precursor ▪ Developed on a humanitarian nonprofit basis ▪ Purpose: To alleviate vitamin A deficiencies in

developing world

Making GMOs - Definitions

• Transgenic organisms – genes are transferred from one organism to

another – Done by genetic cloning

• Cigenic: Used to describe genes transferred within a species

Biotechnology – part of GMOs

• Wide range of methods that manipulate organisms or their components to produce a product

– Examples: isolating enzymes or producing wine, cheese, or yogurt

Where are GM crops?

• GM crops are grown in approximately 30 countries

– 90 percent are grown in the United States, Brazil, Argentina, Canada, and India

• In the US: – 93 percent of soybeans – 88 percent of corn – 70 percent of processed

foods in the United States contain GM crop ingredients

Who eats GM foods?

• First GM food for consumptions – Flav Savr tomato

• Production of GM foods shifted toward agriculture – 200 different GM crops are used as food or Livestock feed

• AquAdvantage salmon are the only food source approved for consumption by humans

Most prevalent GM crops: Herbicide-Resistant

• Why have herbicide-resistant GM crops? – Weed infestations destroy 10 percent of crops

worldwide – Herbicides that applied before seeding can be so

efficient that they kill crop plants – Tillage damage from controlling weeds leads to

soil erosion

Highest produced GM food

• Herbicide-tolerant GM crops are the most widely planted

– 70 percent of GM crops are herbicide-tolerant Example: Contain a bacterial gene that confers tolerance to the broad-spectrum herbicide glyphosate (the active ingredient in Roundup)

Second most prevalent GM: Insect-Resistant GM Crops

• Makes plants resistant to agricultural pests

• Insect damage is a serious threat to food production

• Farmers use insecticides to combat issue

Example: Bt Crops

• Insect-resistant GM crops: Bt crops – Bt (Bacillus thuringiensis) is a group of soil-

dwelling bacterial strains ▪ Produce Cry proteins, which are toxic to

insects – Bt crops are engineered by scientists

▪ cry genes are introduced into plant cells ▪ The GM crop plant now can manufacture its

own Bt Cry proteins, which kills the target pest when it eats the plant’s tissue

GM crops for direct consumption

• Examples are Rice, squash and papaya

• Why? To increase consumption of missing nutrients or vitamins whose absence results in some disease.

• Example: Golden Rice – produces vitamin A – Why? 190 million children and 19 million pregnant

women are vitamin A deficient – Between 250,000-500,000 children become blind

due to vitamin A deficiencies and half will die within 1 year of losing their sight. Vitamin A also is essential for the immune system.

– Other methods of introducing vitamin A into the region have not worked

Example: Golden Rice 2

• Golden Rice was genetically engineered to synthesize beta- carotene (precursor to vitamin A)

• Geranlgeranyl-disphosphate is present in rice but the enzymes to convert it are not.

• GM rice introduces the enzymes needed to make beta-carotene

Controversy Regarding Golden Rice

• Clinical trials show that the beta-carotene in Golden Rice 2 was efficiently converted into vitamin A

• Golden Rice 2 is undergoing biosafety testing

• Critics of GM foods suggest that Golden Rice will make farmers too dependent one one type of food

• There are concerns about long-term health or environmental effects

ST 4.2 Methods Used to Create GM Plants

How to Create GM Plants

• Creating GM plants: Two approaches 1. Biolistic method 2. Agrobacterium tumefaciens-mediated

transformation • Both methods target plant cells growing in vitro

– Plant tissue is cultured that is grown in presence of nutrients or hormones

– Cultured cells form clumps that will form roots – The rooted plant develops into a normal plant

Biolistic Method

– Physical method of introducing DNA to cells – Particles of heavy metals (gold) are coated with

the DNA that will transform the cells – These are introduced to cells in vitro using a

gene gun – Plants with gene are selected for the desired

phenotype

Agrobacterium-Mediated Technology

• Utilizes bacteria Agrobacterium tumefaciens, a soil microbe that infects plant cells and causes tumors

• These characteristics are conferred by Ti plasmid

• After Agrobacterium infection, the Ti plasmid integrates a segment of DNA (T-DNA) into plant genome

How scientists use the Ti Plasmid

• Scientists remove T-DNA and replace with cloned DNA of genes desired

• Agrobacterium tumefaciens inserts T-DNA portion of plasmid into host cell’s nuclear genome

How to ensure gene of interest insert into plants

• Use selectable markers – The rates of successful T-DNA integration and

expression are low – Only 1 in 1000 cells is successfully transformed – Selectable markers allow scientists to distinguish

between transformed and nontransformed products (colonies, plants, tissues, etc.)

Negative Selection

• Involves a marker gene: An antibiotic-resistant marker

– Example: Hygromycin-resistance gene

• The marker gene and a promoter are introduced into plant cells along with the gene of interest

• Cells are grown in medium containing hygromycin

• Only cells that express the resistant gene survive

Positive Selection

• Positive selection – One example involves the marker gene

encoding PMI: Phosphomannose isomerase enzyme

– Catalyzes interconversion of mannose 6- phosphate and fructose 6-phosphate

– This enzyme is common in animals but not plants

– Plant cells that express pmi gene survive – Can be positively selected by growing cells on

mannose-containing medium

Example: Roundup-Ready Soybeans

• Roundup-ready soybeans – GM plant with resistance to the herbicide

glyphosate, the main ingredient in Roundup – Glyphosate interferes with EPSPS genes which

synthesize some amino acids in plants – EPSPS are not present in humans

How to make the GM soybean plasmid

– Utilized Agrobacterium strain Ctp4 epsps gene since it is resistant to glyphosate

– E35S – cauliflower mosaic virus promoter – CTP4 – directs EPSPS into chloroplasts – Biolistic technique introduced the plasmid – Selected for by spraying plants with glyphosate – Farmers can spray Roundup on crops and kill

only weeds, not their crop of soybeans

Method of making Round-up Ready Soybeans

How Golden Rice 2 was made

• Ti plasmid was used to create Golden Rice 2 – Plasmid contained several genes

▪ crtl gene: Carotene desaturase cloned from bacteria

▪ Psy gene: Phytoene synthase cloned from maize

▪ Pmi gene: Phosphomannose isomerase cloned from E. coli – selectable marker

▪ Glu promoter directs transcription in endosperm

▪ Ubi1 promoter allows transcription in all tissue

Method of making Golden Rice 2

Gene editing • Make single nucleotide/single gene changes/deletions without

introducing foreign DNA

• Not considered genetically modified

• Using – ZFN – zinc finger nuclease – TALEN – transcription activator-like effector nuclease – CRISPR-Cas

• Examples: – Potato with increased storage life – Pigs resistant to viruses – Double-muscled pigs – White button mushroom that does not turn brown – already

in stores

The Future of GM Foods: Transgenic salmon

• Transgenic salmon is likely to receive marketing approval soon

• The AquAdvantage salmon grows twice as fast as a non- GM Atlantic salmon, reaching market size in half the time.

ST 4.3 GM Foods Controversies