ARS | Publication request: Varied Growth, Biomass and Cellulose Content in Tobacco Expressing Yeast-Derived Invertases

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2006
Publication Date: June 6, 2006
Citation: Canam, T., Park, J., Yu, K.Y., Campbell, M.M., Ellis, D.D., Mansfield, S.D. 2006. Varied growth, biomass and cellulose content in tobacco expressing yeast-derived invertases. Planta 224:1315-1327.

Interpretive Summary: The biochemical and genetic basis underlying plant growth and yield are poorly understood. From a simplistic view, we know that energy captured in the leaf is converted to sugar and other carbohydrates in the leaf and transported through the plant to areas where it is needed for growth, structural support or storage. This paper focuses on experiments which were conducted to manipulate sugar levels in the plant to increase the amount of cellulose, the primary material in a plant cell wall. Genes encoding two classes of an enzyme, invertase, which cleave sugar into its two monosaccharides, fructose and glucose, were introduced into tobacco plants to determine if the over expression of these genes could increase cellulose content. The theory was that since cellulose is a long chain of glucose molecules, increasing glucose levels would increase cellulose production. The genes encoding invertase were put into tobacco plants in such a way that over expression of the enzyme occurred either all over the plant or specifically in the vascular tissues such as the stem. Plants over expressing the invertase enzymes tended to be shorter than controls however, some lines had significant increases in biomass, expressed as increased biomass/height. One line had an 88% increase in biomass/height and an increase in stem diameter of over 40%. These results indicate that the over expression of invertase in plants has many varied effects, which can in some cases include increased cellulose but at a cost of shorter plants.

Technical Abstract: The effects of the expression of yeast-derived apoplastic (AI) and cytosolic (CI) invertases on biomass and structural carbohydrate accumulation in tobacco (Nicotiana tabacum cv. Xanthi) were evaluated. Transgenic tobacco plants expressing AI or CI under the control of either a tandem repeat of the Cauliflower Mosaic Virus 35S promoter (2X35S), or a promoter that drives xylem-localised expression (Petroselinum crispum 4-coumarate:CoA ligase promoter; 4CL) were generated. Yeast invertase transcript levels, invertase protein, enzyme activity, growth parameters and both structural and soluble carbohydrates of stem tissue of all transformed lines were quantified. Transgenic tobacco lines expressing invertase under the control of 4CL displayed severe growth retardation with both yeast-derived isogenes. Similarly, several transformed lines expressing either AI or CI regulated by the 2X35S promoter were also shorter than wild-type (WT) plants. Despite the decreases in height, some transformed lines had significant increases in biomass. One line (2X35S::AI-1) had a biomass/height increase of 88% and an increase in stem diameter of over 40%, while a second line (2X35S::CI-5) had a biomass/height increase of 21%. A separate line (2X35S::AI-2) had a 36% increase in cellulose content, while two others (4CL::AI-2 and 4CL::AI-3) displayed significant decreases in cellulose content, The observed phenotypes can be in part explained by the levels of foreign invertase present, subcellular localization and the carbohydrate status of the tissues.