Altered fructan accumulation in transgenic Lolium multiflorum plants expressing a Bacillus subtilis sacB gene

Abstract.

Ryegrasses, like many C3 plants, accumulate fructan, which plays an important role in assimilate partitioning, as the major non-structural storage carbohydrate. The present study describes the transformation of a Bacillus subtilis sacB gene, with vacuolar targeting signal sequences and driven by constitutive promoters, into Italian ryegrass (Lolium multiflorum Lam.) by microprojectile bombardment of embryogenic suspension cells. The expression of the chimeric sacB genes in transgenic ryegrass plants and the concomitant accumulation of low levels of bacterial levan were found to substantially distort the native grass fructan synthesis pattern. High-molecular-weight native fructan was depleted, and the pattern of accumulation of oligosaccharides in the range of 5–35 degree of polymerization was altered. The levan-accumulating sacB-transgenic ryegrass plants had a lower level of total fructose, unchanged sucrose levels, and slightly reduced hexose levels compared to the isogenic controls. Growth of the levan-accumulating sacB-transgenic ryegrass plants slowed down with the onset of the reproductive phase. Flowering plants were stunted and had narrower leaves and poorly developed roots. The association between the manipulated fructan metabolism and the phenotype of the levan-accumulating sacB-transgenic ryegrass plants is discussed.