Genetic Engineering in Agriculture, Part 2

Genetic engineering in agriculture overcomes some of the limitations of traditional agriculture. Until now, we’ve spent enormous efforts to adapt the environment to the plant. That’s what a farm is, an adapted environment with the purpose of maximizing the growth of a plant. Now, we have the possibility of being able to adapt the plant to fit the environment. Here I will list the limitations of traditional methods that genetic engineering in agriculture overcomes. Also, I’ll list some of the genetically modified plants in widespread use over the world today.

1. Limitation number one: in traditional agriculture they select specific traits (genes) for crosses, but at the same time other hidden genes that are not desirable may also be transferred. Using genetic engineering in agriculture, single genes are transferred.
   
2. Limitation number two: there are many genes in nature that can’t be crosses into crop plants because they are in different species. Using genetic engineering in agriculture, genes from any organism can be transferred.
   
   
3. Limitation number three: traditional agriculture is slow. Genetic engineering is rapid. You can see results in weeks.
   
   
4. Limitation number four: the ecological thrust of agriculture has remained to use genetics and technology to adapt the environment to the plant. With genetic engineering, the plant can be adapted to the environment.
   

Genetically modified plants are in widespread use. I’ll give you three examples.

Plants That Make Their Own Insecticide

Insecticides are chemicals that kill insect pests. The problem with insecticides, however, is that many of them are not specific. They target many insects, not just the pest. In addition, some insecticides are toxic to the environment in other ways. Insect larvae (the immature stage of insects) eat, among other things, bacteria.

There is a bacterium called Bacillus thuringiensis that has a gene that defends itself against insect larvae. This gene codes for a protein that binds to the insect larvae’s intestine, and makes it loose all of its fluids. The insect gets chronic diarrhea and dies.

The gene coding for this toxin protein has now been introduced to corn, cotton, soybeans and tomato cells. These cells were cloned to make plants that express the toxin in the leaf. As a result, the insect caterpillars land on the leaf, begin to eat and die very quickly. The population of this pest goes way down.

This technology has reduced insecticide use by 90%. This is an environment-friendly use of genetic engineering in agriculture.

Plants Resistant to Herbicides

Weeds can be killed by repeated applications of herbicides (chemical that kill weeds). These chemicals, however, very often kill beneficial plants as well, and even some crops. These are non-specific toxins. Great care is needed to use herbicides properly.

Genes had been identified from bacteria and other sources that code for proteins that break down herbicides. That’s how the bacteria survive to them. These genes had been isolated from the bacteria and put into cotton, corn, soybeans, rice, etc. As a result, these modified crops are now resistant to the herbicide. The herbicide can be applied without any risk of damaging the crop. These crops are in widespread use all over the world.

Nutritionally Rich Rice

Rice grains are deficient in their protein, in terms of their amino-acid balance. There is an ongoing effort to improve that. In addition, rice does not make a substance called beta-carotene. People require beta-carotene, which gets converted into vitamin A, in their diet. Rice plants do not have the gene to make beta-carotene. As a result, about 250000 children go partially blind each year. They are eating rice, and they don’t get enough beta-carotene in their diet.

Other organisms have the genes coding for enzymes that can produce beta-carotene through a biochemical pathway. Ingo Potrykus isolated DNA for each one of these enzymes. One of them was from a bacterium, the other genes happened to be from a daffodil plant. One by one, over a period of a decade, he took each one of these genes and introduced them into a rice plant, along with a promoter that would stimulate gene expression in the developing rice grain.

The result is a rice plant that made grains with beta-carotene. These plants are now being crossed with local varieties all over the world to make the beta-carotene phenotype part of rice that is used in different regions of the world.

Genetic Engineering in Agriculture

Let’s talk about genetic engineering in agriculture. As we know, genetic engineering allows transferring genes from one organism to another. How is this useful in agriculture? We’re faced with a challenge over the next 50 years: feeding an ever expanding human population. According to UN estimates, human population will level off at about 10 billion people. Can genetic engineering in agriculture help?

A real problem in agriculture that existed for millennia is that most plants cannot grow in salty soils. When soil is irrigated, that is when people bring water to dry soils, the water also brings salts. This temporarily allows plants to grow, and normally these small amounts of salts get removed from the soil by rainfall. In dry climates, however, there isn’t much rain. As time goes on, salt builds up.

Salt build up has always been a major problem in agriculture. It led to the fall of civilizations. For example, the Mesopotamians fell as a civilization largely because of salt build up in their soil. Today, it is estimated that up to 65 thousand acres of farmland a day are lost to excess salt build up. The soils are essentially rendered unusable.

Salt is toxic to plants in two ways. First, salt impairs the roots from taking up water. Second, salt blocks several of the enzymes involved in important processes. How does it do that? It alters the way that these proteins fold, and if an enzyme folds incorrectly it won’t be able to do its function. The particular enzymes I’m talking about are involved in making proteins, and also some involved in photosynthesis. Photosynthesis is the process by which a plant converts solar energy into stored energy in the form of sugars.

Few plants in the world can thrive in very salty soils. Certainly, not the major crops (rice, wheat and corn). Finding a gene for salt tolerance in these crop plants is unlikely. If you go to the crop seed bank, it’s likely that you’re going to find a variety of rice that has a mutation that makes it tolerant to salt.

Scientists always use “model organisms” to do research. The model plant is a tiny mustard like plant, called Arabidopsis. Arabidopsis is a model for the genomes of the major crops. Arabidopsis does all the things that the major crops do. It has roots, stems, leaves, flowers and all those things. It is useful to study it because we can grow it in a greenhouse near a laboratory and we know its entire genome.

In the 1990’s, Eduardo Blumwald found that Arabidopsis has a gene that is expresses as a protein which suck ups salt form the soil, and put it into storage depots inside of cells called vacuoles. These particular cells are in the leaves of the plant. This might be a pretty good way to tolerate salt. The salt would never get into the rest of the cell.

The problem comes when the salt build up in the soil is very high, as happens in soils that had been rendered unsuitable for agriculture. There isn’t enough of this protein, so the excess salt leaks out of the vacuoles and gets into the rest of the cells.

Using genetic engineering, Blumwald has added a vector with a very active promoter (a section of DNA that turns on a gene) beside the gene that allows the salt to be stored in vacuoles. So, the expression of this gene would be enhanced. When he made transgenic plants using this vector, the genetically modified Arabidopsis was able not just to withstand salty soil, but to thrive in it. What an amazing thing!

Blumwald didn’t really want to grow Arabidopsis on salty soils, but to get this gene into crop plants. Genetic engineering allows transferring genes from one organism to another. When the active salt-tolerance gene from Arabidopsis was put into a tomato plant, it became very salt-tolerant. A normal tomato plant would wither and die in a salty soil, whereas the modified tomato plants would be just fine. What’s more, the salt was in the leaves, the tomato fruits were just fine.

While tomatoes are important, they are not nearly as important as the major grain crops. So, Blumwald and others are busily trying to transfer this salt-tolerance gene from Arabidopsis to rice, wheat and corn.

This may make salty soils in the world usable for farming. Salt-tolerant transgenic plants may make deserts bloom again.

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