Ononitol and pinitol production in transgenic soybean containing the inositol methyl transferase gene from Mesembryanthemum crystallinum

Although cyclitols are a major portion of carbohydrates in plants, surprisingly little is known about their metabolism. In the halophytic iceplant ( Mesembryanthemum crystallinum), ononitol is produced through the action of inositol methyl transferase (IMT), which transfers the methyl group from S-adenosyl- l-methionine to myo-inositol. Through an epimerase reaction, ononitol is then converted to pinitol. In an attempt to modify and study cyclitol production in a pinitol-producing glycophytic plant, an imt gene from M. crystallinum was introduced into soybean ( Glycine max (L.) Merr. cv. ‘Jack’) embryogenic tissue using particle bombardment. Southern and northern hybridization analyses showed that all of the transgenic clones contained a low copy number of the introduced plasmid DNA and imt mRNA was present. In transgenic embryogenic soybean tissues, ononitol levels were increased 10–80-fold compared to non-transgenic tissues. Pinitol was first produced late in somatic embryo development in both transgenic and non-transformed tissues, indicating that the epimerase responsible for the conversion of ononitol to pinitol was developmentally regulated. The increase in ononitol levels in transgenic developing embryos led to 2–6-fold higher pinitol levels in transgenic embryos compared to non-transformed tissues. In leaves from mature plants, however, pinitol levels were not significantly different bewteen imt-containing and non-transformed tissues.