SPEAKER: The last technology that has been developed-- and actually, it's a collection of technologies, which has probably had the greatest impact, not only on traditional plant breeding, but tremendous political and economic impact on the world today-- is the development of transgenic plants. First, let's talk about, how do you make a transgenic plant? And you can see, you have to utilize several of the technologies we've already discussed.
In order to develop a transgenic plant, we're going to walk through five steps. The first step is the transfer of genes from one organism to another using the technology we talked about just a few minutes ago that allows us to cut, paste, and clone genes. Once we have these genes, we can introduce these genes into plant species in two ways. One way is using the bacterium, microbacterium.
Second way is actually by using what's called a gene gun. Basically, you coat the DNA carrying the genes on a projectile particle, and you literally fire that particle through a biolistic process through the wall of a plant's cell. The DNA comes off from the particle, enters the cell, and the plant's able to incorporate that DNA.
Once we've transferred foreign DNA into a plant cell, we must select and identify transgenic cells. This is done primarily by growing those cells in a culture medium using tissue culture technologies.
Often, in order to identify the transgenic cells readily in the culture medium, we add a selectable marker, a marker such as herbicide tolerance or antibiotic resistance to the gene so that in the culture solution, we can add the herbicide or the antibiotic and only the transgenic cells are able to grow and develop. Once we've selected cells that, in fact, are growing within this culture medium and a transgenic, we need to regenerate these cells back into whole plants, again, using standard tissue culture technologies.
After regenerating plants carrying transgenes, it's still not a sure sign that the plants produced will express that gene and will actually show the trait of interest. So then we have to grow those plants out in the field, select and measure and determine that, in fact, the gene that has been inserted is functioning.
There are lots of reasons why genes inserted into plants don't function. Sometimes they insert the regions of the plant genome that just won't work. Other times, the genes are there, they're inserted into the plant, but the plant really doesn't recognize that this is a plant gene and this is something that I should be transcribing to produce proteins from.
Finally, once we've identified plants that are carrying transgenes and expressing traits controlled by those transgenes, we've still got to convert that plant into a useful variety. This is done most often by backcrossing. And by using marker-assisted backcrossing, this can be done in a number of one to two years rather than five to 10 years. But still, the process of transferring that transgenic material into a useful elite variety must be done.
And of course, once you've converted that transgene into a useful variety, you have several years that you must go through for testing in multiple locations over diverse environments to make sure that the new variety is stable, productive, useful, and desirable. If you're interested in more detail about the process of how to make a transgenic plant, there's another series of animations available in the web link section of the CyberTower room.
Since 1996, there have been a number of transgenic crop varieties developed and released. A lot of these crop varieties never made it through the stages of testing and regulatory approval, either because of undesirable characteristics carried along with the transgene or because of lack of performance of the new transgenic varieties compared to traditional varieties. However, a few of the transgenic varieties have been developed, released, commercialized, and are very, very successful.
From 1996 to 2002, the acres grown to transgenic crops has increased from 1.7 million back in 1996 to 58.7 million in 2002. Most of these transgenic crops are grown in the US, Canada, Argentina, and China. And for the most part, transgenic soybeans engineered to be resistant to the herbicide Roundup, cotton engineered to be resistant to the cotton bollworm insect, and corn engineered to be resistant to the European corn borer and related species account for most of the acres.
We've looked at development of several molecular technologies and how they've impacted on traditional plant breeding. Next, we'll go back and do a comparison of sort of three stages of the history of plant breeding, the domestication of crops species, traditional or classical plant breeding, and transgenic technologies.
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Plant Breeding: Then and Now provides an overview of plant breeding techniques, from early crop domestication to the latest developments in biotechnology methods. Plant breeding is one of the oldest scientific disciplines that has developed over thousands of years. Discover how recent developments in biotechnology are changing the science and methods of plant breeding.
This video is part 4 of 6 in the Plant Breeding: Then and Now series.