Lipoic acid-an unique plant transformation enhancer

Including lipoic acid (LA) in culture media during Agrobacterium transformation processes of four crop species has significantly improved the transformation methods of the crops, even for previously recalcitrant genotypes. Plant transformation efficiency of soybean was significantly increased from 0.6% to 3.7% and tomato from 29.8% to 87.0%. Transformation efficiency was doubled from 2.8% to 5.7% in wheat. The frequency of glyphosate-resistant embryos had a significant increase from 41.4% to 61.2% in cotton. Regeneration of non-transgenic shoots under selection ("shoot escapes") was significantly reduced in tomato from 91.5% to 46.2% while in soybean from 92.0% to 72.0% under optimal conditions. This study also demonstrated that the increase of transformation efficiency in tomato was accompanied by as much as a significant 2-fold reduction in severity of browning of Agrobacterium-infected plant tissues and up to a significant 3-fold increase in the percentage of explants with a high level of transient gene expression. LA application in plant transformation has enabled the resolution of three common problems in plant transformation: browning or necrosis of the transformed cells or tissues, difficulty in regenerating transformed cells or tissues, and shoot escapes, which severely limit the number of transgenic plants that can be regenerated.