Genetic Engineering of Glycinebetaine Production toward Enhancing Stress Tolerance in Plants: Metabolic Limitations1

• Published in: Plant physiology (Bethesda) Vol. 122; no. 3; pp. 747 - 756
• Main Authors: Huang, Jun, Hirji, Rozina, Adam, Luc, Rozwadowski, Kevin L., Hammerlindl, Joe K., Keller, Wilf A., Selvaraj, Gopalan
• Format: Journal Article
• Language: English
• Published: American Society of Plant Biologists 01.03.2000
• ISSN: 0032-0889; 1532-2548

Glycinebetaine (betaine) affords osmoprotection in bacteria, plants and animals, and protects cell components against harsh conditions in vitro. This and a compelling body of other evidence have encouraged the engineering of betaine production in plants lacking it. We have installed the metabolic step for oxidation of choline, a ubiquitous substance, to betaine in three diverse species, Arabidopsis, Brassica napus , and tobacco ( Nicotiana tabacum ), by constitutive expression of a bacterial choline oxidase gene. The highest levels of betaine in independent transgenics were 18.6, 12.8, and 13 μmol g −1 dry weight, respectively, values 10- to 20-fold lower than the levels found in natural betaine producers. However, choline-fed transgenic plants synthesized substantially more betaine. Increasing the choline supplementation further enhanced betaine synthesis, up to 613 μmol g −1 dry weight in Arabidopsis, 250 μmol g −1 dry weight in B. napus , and 80 μmol g −1 dry weight in tobacco. These studies demonstrate the need to enhance the endogenous choline supply to support accumulation of physiologically relevant amounts of betaine. A moderate stress tolerance was noted in some but not all betaine-producing transgenic lines based on relative shoot growth. Furthermore, the responses to stresses such as salinity, drought, and freezing were variable among the three species.