The esterification status and the length of acidic stretches of homogalacturonan is critical for plant biomass processing.

The cell wall recalcitrance to enzymatic hydrolysis is the main bottleneck for the industrial scale-up of biomass processing and bioconversion to fermentable sugars. Pectin stabilizes the cell wall by calcium-mediated cross-links formed by stretches of acidic homogalacturonan (HGA). We have demonstrated the length reduction of HGA in Arabidopsis and tobacco through the expression of a fungal polygalacturonase (PG) and the reduction of the de-methylated form of HGA in Arabidopsis and wheat through the expression of an inhibitor of pectin methylesterase enhance the tissue digestibility and reduce the need of acid pre-treatment used before biomass processing. We show here that a better digestibility of the plant tissue is consistently correlated with a lower content of de-methylated stretches of HGA in the cell wall. This can be achieved by transforming plants not only with fungal PGs and inhibitors of pectin methylesterases but also by other pectic enzymes of different origin. Plants with reduced quantities of the acidic form of HGA may also be genetically selected.