Transgenic modification of potato pectic polysaccharides also affects type and level of cell wall xyloglucan

BACKGROUND: Genes encoding pectic enzymes were introduced into wild-type potato Karnico. Cell wall materials were extracted from Karnico and transgenic lines expressing β-galactosidase (β-Gal-14) or rhamnogalacturonan lyase (RGL-18). Pectic polysaccharides from the β-Gal-14 transgenic line exhibited rhamnogalacturonan-I structural elements with shorter galactan side chains, whereas the RGL-18 transgenic line had less rhamnogalacturonan-I structures than Karnico. Xyloglucan in primary cell walls interacts with pectin and other cell wall polysaccharides and controls cell growth. RESULTS: Xyloglucan extracts from transgenic lines had different levels of monosaccharides compared to wild-type. Most XXGG-type xyloglucans from Karnico and RGL-18 alkali-extractable extracts predominantly consisted of XXGG and XSGG building blocks. Karnico and RGL-18 4molL-1 extracts had small proportions of the XXXG-type xyloglucan, whereas β-Gal-14 extracts also contained the XXXG-type xyloglucan. The peak ratios of XSGG/XXGG were 1.9, 2.4 and 1.1 for 4molL-1 extracts of Karnico, RGL-18 and β-Gal-14 lines, respectively. CONCLUSION: After transgenic modification on pectin, the xyloglucan building blocks may have been changed. The β-Gal-14 lines mostly present XXXG-type repeating units instead of the XXGG-type in 4molL-1 extracts. The ratio of XSGG/XXGG repeating units also changed, indicating that the transgenic modification of pectin altered xyloglucan structure during plant development.