title: Down-regulating alpha-galactosidase enhances freezing tolerance in transgenic petunia.
abstract: Alpha-galactosidase (alpha-Gal; EC 3.2.1.22) is involved in many aspects of plant metabolism, including hydrolysis of the alpha-1,6 linkage of raffinose oligosaccharides during deacclimation. To examine the relationship between endogenous sugars and freezing stress, the expression of alpha-Gal was modified in transgenic petunia (Petunia x hybrida cv Mitchell). The tomato (Lycopersicon esculentum) Lea-Gal gene under the control of the Figwort Mosaic Virus promoter was introduced into petunia in the sense and antisense orientations using Agrobacterium tumefaciens-mediated transformation. RNA gel blots confirmed that alpha-Gal transcripts were reduced in antisense lines compared with wild type, whereas sense plants had increased accumulation of alpha-Gal mRNAs. alpha-Gal activity followed a similar trend, with reduced activity in antisense lines and increased activity in all sense lines evaluated. Raffinose content of nonacclimated antisense plants increased 12- to 22-fold compared with wild type, and 22- to 53-fold after cold acclimation. Based upon electrolyte leakage tests, freezing tolerance of the antisense lines increased from -4 degrees C for cold-acclimated wild-type plants to -8 degrees C for the most tolerant antisense line. Down-regulating alpha-Gal in petunia results in an increase in freezing tolerance at the whole-plant level in nonacclimated and cold-acclimated plants, whereas overexpression of the alpha-Gal gene caused a decrease in endogenous raffinose and impaired freezing tolerance. These results suggest that engineering raffinose metabolism by transformation with alpha-Gal provides an additional method for improving the freezing tolerance of plants.
mesh_terms: D000064:Acclimatization; D050260:Carbohydrate Metabolism; D005615:Freezing; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D018551:Solanum lycopersicum / Q000201:enzymology; D032306:Petunia / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D013816:Thermodynamics; D000519:alpha-Galactosidase / Q000235:genetics* / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D000519:alpha-Galactosidase