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.