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2-Plants: UK study revealed chloroplast gene flow in rapeseed

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TITLE:  Field study on transgene release
SOURCE: ISB News Report, by John T. Lohr
DATE:   May 1999

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A fundamental concern about genetically engineered plants is the potential for negative consequences arising from the transmission of transgenes to wild relatives. In the U.S., most major commodity crops are not native and thus lack wild-type relatives. However, in many other countries, native weed relatives exist and transgene release is an issue. Rapeseed (canola) is an example.

Most transgenes are added to chromosomal genes and thus will be present in the pollen of the transgenic plant. One strategy to eliminate transfer by pollen is to add the transgene to chloroplast DNA. Chloroplasts contain genes for their own replication and enzymes, and can be genetically engineered. Maternally inherited chloroplasts are not, in most cases, present in pollen, therefore, genetic engineering of chloroplasts should prevent the transfer of transgenes.

To test the theory, Scott and Wilkinson (1) studied a 34-Km region near the Thames River, U.K. where oilseed rape is cultivated in the vicinity of a native weed, wild rapeseed. Oilseed rape, the cultivated form of Brassica napus, and the wild rapeseed (B. rapa) are capable of exchanging pollen to produce viable hybrids. The study was designed to determine whether oilseed chloroplasts could be transferred to wild rapeseed, and how long the hybrids and maternal oilseed plants would survive in the wild.

To identify chloroplasts, the authors created primers specific to chloroplast DNA non-coding regions. In PCR experiments, oilseed chloroplasts produced a single amplification product of 600 bp, whereas wild rapeseed produced a 650 bp product. In all cases, the chloroplasts from hybrid plants contained the PCR product of the maternal line demonstrating that they are not transferred in pollen.

Another route of transgene release is accidental distribution of seed. This occurs during transportation, seeding, and harvesting. Oilseed that is spread outside cultivated fields can cross with weeds allowing the transgene to enter the feral population.

The authors studied the frequency of hybrid formation and viability of oilseed and hybrids in non-cultivated areas over a three-year period. Their studies show that oilseed has a very low survival rate outside cultivated fields. On average, only 12-19% of oilseed survived each growing season. At the same time, a very low level of natural hybridization was observed (0.4-1.5%). Taken together, the results indicate that there is a very low, but real, possibility of transgene movement into feral populations of maternal lineage. However, the persistence of the maternal line in the wild will be of limited duration.  Source

Scott SE, and Wilkinson MJ. 1999. Low probability of chloroplast movement from oilseed rape (Brassica napus) into wild Brassica rapa. Nature Biotechnology 17:390-392.

John T. Lohr
Assistant Director, Education & Outreach
Utah State University 


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