Clean-gene Technology: Helping adaptation of transgenic crops

Transgenic plants that contain the desired gene of interest but lack the selection marker gene used in its production are termed “clean” and the methods utilized in their production are referred to as “clean-gene technology”.

The ever-increasing world population has created two major problems: more mouths to feed and less land to farm. Transgenic plants can help especially where classical breeding lacks solution (e.g. limited availability of stable and durable genetic source of resistance).

However, plant transformation technologies require selectable marker genes to produce transgenic plants but such genes are of no value thereafter. In fact, marker genes in transgenic plants are perceived to pose potential bio-safety problems. The products of some marker genes may be toxic or allergic.

The antibiotic resistance might be transferred to pathogenic microorganisms in the soil. There is a possibility of creation of superweeds that are resistant to normally used herbicides. An easy and efficient way to develop genetically-modified crops that are ‘biosafe’ is now available.

People worldwide are reluctant to accept genetically-modified foods because they might contain genes resistant to antibiotics or herbicides, which could be harmful.

Clean-gene Technology

Transgenic plants that contain the desired gene of interest but lack the selection marker gene used in its production are termed “clean” and the methods utilized in their production are referred to as “Clean-gene Technology”.

This means, the crops do not carry what are called ‘selectable marker genes’, such as genes resistant to antibiotics or herbicides. Clean-gene technology is a process that transforms plants using two separate vectors, one carrying the transgene and the other carrying the selectable marker gene.

The transgene has desirable feature that needs to be added, and selectable marker gene allows scientists to identify transgenic plants. During transformation, a bacterium called Agrobacterium tumefaciens integrates two vectors.

In roughly half the cases, the two vectors are integrated at different locations in the plant genomes. This means the vectors can be segregated from each other at the next generation.

Methods of removing marker

There are several proven methods of eliminating selectable marker genes:

1. marker gene excision consisting of, (a) intra-genomic relocation of transgenes via transposable elements, and (b) site-specific recombination systems;
2. intra-chromosomal recombination;
3. Gene replacement or Targeted gene replacement; and
4. transformation with multiple T-DNAs, which could result in linked and/or unlinked co-integration of transgenes.

Unlinked transgenes are then segregated out during meiosis.

Advantages of Clean-gene Technology

Transgene technology provides powerful tool for developing traits that are otherwise difficult to achieve through conventional method. Therefore there is need to adopt transgene technology to develop transgenics. Transgenic plants with desired characters can help us to meet the food demand by increasing yield and productivity.

The development of transgenic plants requires use of selectable marker genes, as efficiency of plant transformation is less than optimal for many important species, especially for monocot as durum wheat (Triticum turgidum var durum).

Many concerns are associated to the persistence of marker genes in plants used for field cultivation. A real concern is the potential for a transgene to move from a crop plant to its wild relative thereby creating a weed that may be hard to control by the use of available herbicides. Another important concern is the possibility of human health risks.  Clean-gene technology is the solution to this problem.

Prospects of Clean-gene Technology in Pakistan

Previously, selectable marker genes in transgenic plants prevented acceptance of genetically-modified crops in both the developing and developed world. But researchers in China, India, the UK and the USA are now using clean-gene binary vectors for crop improvement. This is good news as it generally takes years for new technologies to be taken up in crop transformation programmes.

But the quality, reproducibility and safety of the safe clean-gene technology means that it’s set to become the international standard for producing genetically-modified plants.

The clean-gene technology was developed using rice. However, the technology is generic and can be applied to all sexually propagated plants – maize, wheat, millet, cowpea, sorghum, trees and vegetables.

The clean-gene technology has great potential for Asian and African research programmes that aim to improve rice by genetic methods. It can also be readily used to improve crops grown by poor farmers in China, India and South Africa. Clean-gene also improves important staples, such as maize and wheat, orphan crops, such as millet, cowpea and sorghum, and many fruits, nuts and vegetables.

Laboratories in Asia, Africa, the USA and the UK are already using this process. The John Innes Centre in the UK has already produced genetically-modified rice resistant to nematodes and free of selectable marker genes. Crops grown by millions of poor farmers in China, India and South Africa, could be readily improved by clean-gene technology.

Now people in Pakistan are also growing GMO crops. Transgenic Soybean, Bt cotton and maize are being grown in Pakistan. We can improve our agricultural GDP by adopting transformation biotechnology. Only problem is biosafety issues caused by selectable markers. This issue can be resolved by using “Clean-gene technology”. So we should develop transgenes by using clean-gene technology to improve our agricultural productivity. 

This article is jointly written by Rahil Shahzad, Shakra Jamil, and Adeela Sahar. The authors are from Agricultural Biotechnology Research Institute, AARI Faisalabad