Evaluation of both targeted and non-targeted cell wall polysaccharides in transgenic potatoes

In this study, we analyze 31 transgenic lines and their respective untransformed background lines to determine the transgene effects on targeted structures including the pectin components rhamnogalacturonan I (RG-I) and homogalacturonan (HG), neutral side chains (galactan/arabinangalactan), acetylation of pectin, and cellulose level. Modification arising from the pectin backbone- or pectin side chain transgenic lines either increased or decreased the HG:RG-I ratio, side chain length, and methyl esterification of pectin in the tuber cell wall. The pectin esterification transgenic line exhibited only limited side effects. The cellulose level-targeting transgenic lines yielded an unexpectedly high HG:RG-I ratio and longer pectic side chains. These results clearly demonstrate that in effects of a transgene are not restricted to the direct activity of the targeted enzyme but have consequences for the structure of the cell wall matrix. Analysis of whole cell wall structure is therefore necessary to assess the complete effect, direct and indirect, of a transgene.