Genetic Improvement (Biotechnology) and Variety Selection
Parts of a Gene - Promoter
A gene has two main components which you need to consider when selecting a specific crop variety. The first is called a promoter sequence and is much like the on/off dimmer switch for a light. Just as with a light where a dimmer switch will turn it on or off, as well as increase or decrease the brightness intensity, a promoter in a gene also turns it on or off and determines how much protein is eventually produced from that gene.
Parts of a Gene - Coding Region
The second gene component is called the coding region. The coding region is similar to a blueprint which determines the layout of a new building. In a gene, the coding region determines the type of protein produced.
Modifying Genes to Make New Traits
Let's continue with our BT example to understand these two concepts. If a scientist wants to affect which plant tissue the BT insecticidal protein will be expressed in, s/he can exchange the promoter region. In the image below, the 35S promoter is one which turns on a gene in all plant tissues. It is replaced with one that turns on genes only in green tissue, a Pep Carboxylase promoter. The result is a BT corn plant which has insecticidal proteins only in its green tissue.
Now let's see what happens if we modify the coding region of a gene. In the image to the right, we see two different gene constructs, but both are for BT insecticidal proteins. Both have the same promoter, 35S, so their genes will be expressed in all plant tissues. However, in looking closely, we see they have two different coding regions. Gene A has the cry1A(b) coding region, while Gene B has the cry 9C coding region. Although both are BT proteins, their chemical makeup will be slightly different and impact their target insects differently.
Know Your Genes to Pick Your Variety
To best maximize your profits, you'll need to pick the variety which has the traits of most interest for your farming environment and practice. When alternating resistance modes of actions, be sure to check out your variety's coding region. This can sometimes be tricky to decipher. Your particular variety may have stacked genes, which means it contains more than one transgene event. A good online resource is the AgBios site, where you can search for all approved biotech crops in the GM database. You can also discuss this with your crop consultant or seed sales representative.
Various Bt genes have been used in several crop species to provide resistance to pests. Below is a table of Bt events that have been approved in the United States.
Table of Bt events approved in the United States. Source www.agbios.com
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Deana Namuth-Covert, PhD
279 Plant Science Hall (PLH)
Lincoln NE 68583-0915