Pectin engineering: Modification of potato pectin by in vivo expression ofan endo-1,4-beta-D-galactanase

Potato tuber pectin is rich in galactan (oligomer of beta-1,4-linked galact osyl residues). We have expressed a fungal endo-galactanase cDNA in potato under control of the granule bound starch synthase promoter to obtain expre ssion of the enzyme in tubers during growth. The transgenic plants displaye d no altered phenotype compared with the wild type. Fungal endo-galactanase activity was quantified in the transgenic tubers, and its expression was v erified by Western blot analysis. The effect of the endo-galactanase activi ty on potato tuber pectin was studied by Fourier transform infrared microsp ectroscopy. immune-gold labeling, and sugar analysis. All analyses revealed alterations in pectin composition. Monosaccharide composition of total cel l walls and isolated rhamnogalacturonan I fragments showed a reduction in g alactosyl content to 30% in the transformants compared with the wild type. Increased solubility of pectin from transgenic cell walls by endo-polygalac turonase/pectin methylesterase digestion points to other changes in wall ar chitecture.