Genetic engineering of glycinebetaine production toward enhancing stress tolerance in plants: metabolic limitations.
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 micromol 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 micromol g(-1) dry weight in Arabidopsis, 250 micromol g(-1) dry weight in B. napus, and 80 micromol 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.
Huang
J
J
Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan, Canada.
Hirji
R
R
Adam
L
L
Rozwadowski
K L
KL
Hammerlindl
J K
JK
Keller
W A
WA
Selvaraj
G
G
D000429:Alcohol Oxidoreductases / Q000235:genetics; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001622:Betaine / Q000378:metabolism*; D001937:Brassica / Q000235:genetics / Q000378:metabolism; D002794:Choline / Q000378:metabolism; D015870:Gene Expression; D005818:Genetic Engineering; D009995:Osmosis; D010788:Photosynthesis; D030821:Plants, Genetically Modified / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D010947:Plants, Toxic; D013312:Stress, Physiological / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism
D001622:Betaine; D000429:Alcohol Oxidoreductases; C019888:choline oxidase; D002794:Choline