The disclosure provides methods of engineering plants to modulate galactan content. Specifically, the disclosure provides methods for engineering a plant to increase the galactan content in a plant tissue by inducing expression of beta-1,4-galactan synthase (GALS), modulated by a heterologous promoter. Further disclosed are the methods of modulating expression level of GALS under the regulation of a transcription factor, as well as overexpression of UDP-galactose epimerse in the same plant tissue. Tissue specific promoters and transcription factors can be used in the methods are also provided.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
 This invention was made with government support wider Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in this invention.