JXB Advance Access originally published online on March 1, 2006
Journal of Experimental Botany 2006 57(5):1129-1135; doi:10.1093/jxb/erj133
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RESEARCH PAPER |
Evaluation of the stress-inducible production of choline oxidase in transgenic rice as a strategy for producing the stress-protectant glycine betaine
1Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
2Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan, Canada S7N 0W9
* To whom correspondence should be addressed. E-mail: ray.wu{at}cornell.edu
Glycine betaine (GB) is a compatible solute that is also capable of stabilizing the structure and function of macromolecules. Several GB-producing transgenic rice lines were generated in which the Arthrobacter pascens choline oxidase (COX) gene, fused to a chloroplast targeting sequence (TP) was expressed under the control of an ABA-inducible promoter (SIP; stress-inducible promoter) or a ubiquitin (UBI) gene promoter that is considered to be constitutive. This comparison led to interesting observations that suggest complex regulation with respect to GB synthesis and plant growth response under stress. In spite of the use of the well-studied stress-inducible promoter, the highest level of GB accumulation (up to 2.60 µmol g1 DW) in the SIP lines grown under saline conditions was not as high as in the UBI lines (up to 3.12 µmol g1 DW). Therefore, the use of an ABA-inducible promoter was not more beneficial for de novo production of GB. Interestingly, saline growth conditions enhanced GB accumulation by up to 89% in the SIP lines, whereas up to 44% increase was seen in a UBI line. In all these cases the GB levels were many-fold below the range reported for plant species that produce GB naturally. In spite of lower GB concentrations, statistically greater levels of stress tolerance were found in SIP lines than in UBI lines, suggesting that the stress protection observed in SIP plants cannot be totally explained by the increase in the GB content.
Key words: Choline oxidase, glycine betaine, salt stress, transgenic rice
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