Metabolic engineering of rice leading to biosynthesis of glycinebetaine and tolerance to salt and cold

Genetically engineered rice (Oryza sativa L.) with the ability to synthesiz e glycinebetaine was established by introducing the codA gene for choline o xidase from the soil bacterium Arthrobacter globiformis. Levels of glycineb etaine were as high as 1 and 5 mu mol per gram fresh weight of leaves in tw o types of transgenic plant in which choline oxidase was targeted to the ch loroplasts (ChlCOD plants) and to the cytosol (CytCOD plants), respectively . Although treatment with 0.15 m NaCl inhibited the growth of both wild-typ e and transgenic plants, the transgenic plants began to grow again at the n ormal rate after a significantly less time than the wild-type plants after elimination of the salt stress. Inactivation of photosynthesis, used as a m easure of cellular damage, indicated that ChlCOD plants were more tolerant than CytCOD plants to photoinhibition under salt stress and low-temperature stress. These results indicated that the subcellular compartmentalization of the biosynthesis of glycinebetaine was a critical element in the efficie nt enhancement of tolerance to stress in the engineered plants.