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.