Does Cry1Ac gene harm plants?

A scientific study on the cry1Ac gene has turned controversial, dividing Indian scientists on what appears to be a fundamental issue related to the gene drawn from the naturally occurring soil bacterium, Bacillus thuringiensis. The paper, which was put out by a clutch of scientists including the high-profile Deepak Pental, who recently demitted office as vice chancellor of the University of Delhi, states that expression of the cry1Ac gene in cotton and tobacco is detrimental to growth and development of these plants. It is a finding that comes after Bt cotton has completed a decade-long run in India, a run that its promoters characterise as the most significant agricultural success after the Green revolution of the 1960s.

"Scientists have known about the presence of such abnormalities in tissue culture for the last five decades." -- P Ananda Kumar

The research paper titled “Detrimental effect of expression of Bt endotoxin Cry1Ac on in vitro regeneration, in vivo growth and development of tobacco and cotton transgenics” was published in the June edition of Journal of Biosciences. The peer-reviewed journal is published by the Indian Academy of Sciences. What makes the issue curious is that Pental has been working on GM crops, specially mustard for over a decade. Most of his projects have been sponsored by the Department of Biotechnology.

The authors found that a majority of transgenic plants had very low or undetectable levels of Cry1Ac and that all plants having appreciable levels of Cry1Ac showed developmental abnormalities indicating a correlation between the levels of Cry1Ac expression and growth defects in the plants.

They also showed that if the Cry1Ac was modified so as to be located in one part of the cell, the chloroplast which is the site of photosynthesis in plant cells, they were able to recover plants that showed higher levels of expression of Cry1Ac and did not show developmental abnormalities. Thus, compartmentalisation of Cry1Ac within the plant cell to chloroplasts seemed to alleviate the detrimental effects. The authors also suggested that targeting Cry1Ac to chloroplasts can lead to plants expressing higher levels of Cry1Ac and better insect resistance.

The authors suggest that there is preferential selection taking place during the process of making transgenics, as a result there are reduced chances for plants expressing appreciable levels of Cry1Ac to come through the overall process.

But all this is well-known, say some leading biotechnologist who ask why this is being termed a new finding. P Ananda Kumar, director of the reputed National Research Centre for Plant Biotechnology (NRCPB) of the Indian Council of Agricultural Research, ICAR, points out that the process of raising plants from tissues or cells is carried out under artificial conditions. When one subjects a plant system to artificial environment it is natural to have phenotypic abnormalities, a phenomenon known as “somaclonal variation”. Scientists have known about the presence of such abnormalities in tissue culture for the last five decades. The general procedure followed by the scientific community, both in public and private sector, is to discard such abnormal plants.

Kumar says there are three major limitations in the paper. First, there were no proper controls present in the experiment. “The authors should have compared abnormal cotton plants derived through normal tissue culture with abnormal GM plants expressing Bt protein. As a result they cannot justify what would have been the impact of the same conditions in case the plants were non-GM.”

"Our observations and conclusions are based on experiments with several different constructs and it is a controlled experiment." -- Dr. Pradeep Kumar Burma

After all, several Bt transgenic crops such as cotton, maize, potato, brinjal and tomato have been developed in the last 20 years and are being grown commercially in different parts of the world. In none of these Bt crops, which express high levels of Bt proteins, have abnormalities ever been noticed. The simple reason is that during tissue culture any plants manifesting morphological abnormalities are discarded.

Another limitation of the paper is that a proper scientific analysis to show how Bt protein induces negative effects on plant metabolism has not been provided. The authors have drawn a conclusion based on conjuncture, he says.

Another noted biotechnology scientist reflected similar sentiments but refused to come on record because of his official position. “When the research paper was sent for peer review, one of the reviewers rejected the paper. The paper describes an observation that is daily seen in a laboratory. Publishing it on the pretext that no scientist has published it till date is a weird reason,” he emphasises.

He adds, “Such papers give a platform to the anti-GM lobby to seek a re-think on the technology and create a bad environment for research. It is not surprising that the Indian anti-GM lobby has been widely circulating this paper and questioning the commercialisation of Bt crops because a well-know GM scientist himself is saying this. They are not trying to understand the science of this technology. In fact, GEAC co-chairman Dr A R Reddy has been asked by various scientists and anti-GM people to discuss the paper.”

Interestingly, several scientists working in leading public institutes have criticised the paper and termed it “shoddy” saying that such research brings bad name to the Indian science fraternity. Some say the paper should be withdrawn.

However, Pradeep Kumar Burma, corresponding author of the paper, says he is surprised to learn of this criticism. Responding to the issues raised by Down To Earth, he says, “Our observations and conclusions are based on experiments with several different constructs and it is a controlled experiment which is evident from tables and text stating that results of transformation with a transgene expressing the bacterial gene β-glucuronidase (gus) has been reported.”  The scientists had started working on how Bt protein induces negative effects on plant metabolism, but finding answers to how this mechanism works is going to be a tough task.

Asked why commercial Bt crops such as Bt Cotton and Bt Maize are not showing such traits, Burma says, “In spite of these negative effects, commercial applications can be developed because when you generate thousands of independent events you will be able to generate 1or 2 lines which have levels of expression for the plant to be resistant to the insect and not show the strong phenotypic abnormalities.”

Burma says apart from transgenics with cry1Ac gene, the team had also studied transgenics with many other genes but had not observed this kind of effects.” He adds that the aim of this paper was sharing information and generating knowledge.


 

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