gm-rice/report-2

Bt rice showed signs of dwarfism and other abnormalities.

Manipulated Organism: Rice (Oryza sativa).

Inserted Transgenes: Either the Cry1Ab or Cry1Ac gene from Bacillus thuringiensis (Bt), both of which produce proteins toxic to the larvae of Lepidopteran insects (moths). The Bt gene was controlled with the maize ubiquitin promoter. The genetic constructs also contained the antibiotic resistance genes nptII and hph, as well as the gus reporter gene.

Goal of This Study: Investigate the agronomic and morphological characteristics of transgenic rice plants containing a Bt gene.

Results of This Study:

Eighty rice plants were regenerated from tissue culture and used to establish transgenic lines. "The overall performance of most transgenic lines was inferior to non-transformed controls in terms of plant height, number of productive tillers per plant, number of grains per panicle and seed setting rate.... Some transgenic plants produced small-sized or malformed grains; others had the plant stature of 30% the height of the control" (p. 347-8). Based on several lines of evidence, the authors believe that most of these abnormalities were the result of tissue culturing and/or transformation with Agrobacterium, not the presence of the Bt gene.
However, progeny testing of lines descended from the rice variety Xiushui 11 showed that a dwarf phenotype characterized by "short stature and [a] weak root system" (p. 350) was recessively inherited with the resistance trait. The authors suggest the dwarfism could be (1) caused by a disruptive effect associated with transgene insertion, (2) the result of a mutation located near the transgene on the chromosome (linked traits), or (3) the result of high expression of the Bt toxin. The third possibility seems less likely because, if true, one would expect some stunting even with only one copy of the Bt gene, which was not observed.

Additional Comments: Because the process of genetic engineering tends to create numerous undesirable mutations, plant breeders repeatedly cross GE plants to commercially viable varieties in an effort to separate the desired trait from this genetic "baggage."

Source: Shu, Q., H. Cui, G. Ye, D. Wu et al. (2002). "Agronomic and Morphological Characterization of Agrobacterium-Transformed Bt Rice Plants," Euphytica vol. 126, pp. 345-52.

Author Affiliations: Zhejiang University, China; University of Ottawa, Canada.

Funding: Rockefeller Foundation; China's Ministry of Science and Technology; Yok Ying Tung Education Foundation; Science and Technology Department of China's Zhejiang Province.

Product Status: Not on the market as of 2009.

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Seth JordanAugust 26, 2020