Down‐regulation of a ripening‐related β‐galactosidase gene (TBG1) in transgenic tomato fruits

• Published in: Journal of experimental botany 2001-04, Vol.52 (357), p.663-668
• Main Authors: Carey, Annette T., Smith, David L., Harrison, Elizabeth, Bird, Colin R., Gross, Kenneth C., Seymour, Graham B., Tucker, Gregory A.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Base Sequence; beta-Galactosidase - genetics; Biological and medical sciences; Cell and Molecular Biology, Biochemistry and Molecular Physiology; Cell walls; DNA Primers; Down-Regulation; Economic plant physiology; Enzymes; Fructification and ripening; Fructification, ripening. Postharvest physiology; fruit ripening; Fruits; Fundamental and applied biological sciences. Psychology; Galactans; Growth and development; Lycopersicon esculentum - enzymology; Lycopersicon esculentum - genetics; Lycopersicon esculentum - physiology; Messenger RNA; Plant physiology and development; Plants; Plants, Genetically Modified - enzymology; Plants, Genetically Modified - genetics; Plants, Genetically Modified - physiology; Proteins; Recombinant Proteins - genetics; Ripening; Saccharomyces cerevisiae - genetics; TBG1; tomato; Transgenic plants; Vegetative and sexual reproduction, floral biology, fructification; Yeasts; β‐galactosidase
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jexbot/52.357.663

Exo‐galactanase/β‐galactosidase (EC 3.2.1.23) activity is thought to be responsible for the loss of galactosyl residues from the cell walls of ripening tomatoes. Transgenic tomato plants (Lycopersicon esculentum Mill cv. Ailsa Craig) with reduced exo‐galactanase/β‐galactosidase mRNA were generated to test this hypothesis and to investigate the role of the enzyme in fruit softening. A previously identified tomato β‐galactosidase cDNA clone, TBG1, was used in the experiments. Heterologous expression of the clone in yeast demonstrated that TBG1 could release galactosyl residues from tomato cell wall galactans. Transgenic plants showed a reduction in TBG1 mRNA to 10% of normal levels in the ripening fruits. However, despite the reduction in message, total β‐galactosidase and exo‐galactanase activities were unaffected. Furthermore, there was no apparent effect on levels of cell wall galactosyl residues when compared with the control. It was concluded that during the ripening of tomato fruits a family of β‐galactosidases capable of degrading cell wall galactans are active and down‐regulation of TBG1 message to 10% was insufficient to alter the degree of galactan degradation.