Generation of transgenic wheat (Triticum aestivum L.) accumulating heterologous endo‐xylanase or ferulic acid esterase in the endosperm

Summary Endo‐xylanase (from Bacillus subtilis ) or ferulic acid esterase (from Aspergillus niger ) were expressed in wheat under the control of the endosperm‐specific 1DX5 glutenin promoter. Constructs both with and without the endoplasmic reticulum retention signal (Lys‐Asp‐Glu‐Leu) KDEL were used. Transgenic plants were recovered in all four cases but no qualitative differences could be observed whether KDEL was added or not. Endo‐xylanase activity in transgenic grains was increased between two and threefold relative to wild type. The grains were shrivelled and had a 25%–33% decrease in mass. Extensive analysis of the cell walls showed a 10%–15% increase in arabinose to xylose ratio, a 50% increase in the proportion of water‐extractable arabinoxylan, and a shift in the MW of the water‐extractable arabinoxylan from being mainly larger than 85 kD to being between 2 and 85 kD. Ferulic acid esterase‐expressing grains were also shrivelled, and the seed weight was decreased by 20%–50%. No ferulic acid esterase activity could be detected in wild‐type grains whereas ferulic acid esterase activity was detected in transgenic lines. The grain cell walls had 15%–40% increase in water‐unextractable arabinoxylan and a decrease in monomeric ferulic acid between 13% and 34%. In all the plants, the observed changes are consistent with a plant response that serves to minimize the effect of the heterologously expressed enzymes by increasing arabinoxylan biosynthesis and cross‐linking.