Pectin engineering: Modification of potato pectin by in vivo expression of an endo-1,4-β- d -galactanase

Pectin engineering: Modification of potato pectin by in vivo expression of an endo-1,4-β-d-galactanase

^*Biotechnology Group, Danish Institute of Agricultural Sciences, DK-1871 Copenhagen, Denmark; ^‡Department of Plant Biology, The Royal Veterinary and Agricultural University, DK-1871 Copenhagen, Denmark; and ^§Department of Cell Biology, John Innes Centre, Colney, Norwich NR4 7UH, United Kingdom

Edited by Adrienne Clarke, University of Melbourne, Victoria, Australia, and approved April 28, 2000 (received for review December 27, 1999)

Abstract

Potato tuber pectin is rich in galactan (oligomer of β-1,4-linked galactosyl residues). We have expressed a fungal endo-galactanase cDNA in potato under control of the granule bound starch synthase promoter to obtain expression of the enzyme in tubers during growth. The transgenic plants displayed no altered phenotype compared with the wild type. Fungal endo-galactanase activity was quantified in the transgenic tubers, and its expression was verified by Western blot analysis. The effect of the endo-galactanase activity on potato tuber pectin was studied by Fourier transform infrared microspectroscopy, immuno-gold labeling, and sugar analysis. All analyses revealed alterations in pectin composition. Monosaccharide composition of total cell walls and isolated rhamnogalacturonan I fragments showed a reduction in galactosyl content to 30% in the transformants compared with the wild type. Increased solubility of pectin from transgenic cell walls by endo-polygalacturonase/pectin methylesterase digestion points to other changes in wall architecture.

Footnotes

↵ † To whom reprint requests should be addressed. E-mail: s.sorensen{at}dias.kvl.dk.
This paper was submitted directly (Track II) to the PNAS office.
Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.130568297.
Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.130568297
Abbreviations:

EPG,

endo-polygalacturonase;

FTIR,

Fourier transform infrared microspectroscopy;

GalA,

galacturonic acid;

HGA,

homogalacturonic acid;

PCA,

principal component analysis;

PME,

pectin methylesterase;

RGI,

rhamnogalacturonan I;

UA,

uronic acid