Late-stage changes in the composition of cell walls of maize plants expressing an apoplast targeted, senescence enhanced fungal ferulic acid esterase, and the subsequent effects on tissue saccharification.

Using maize plants expressing an apoplast targeted Aspergillus niger ferulic acid esterase (FAEA), with FAEA driven by a Lolium multiflorum senescence enhanced promoter (LmSee1), we extended measurements of FAEA activity to late-stage senescing plants and measured the stability of FAEA activity following stover storage. The impact of FAEA expression on cell wall hydroxycinnamic acid levels and arabinoxylan (AX) cross-links, and on the levels of cell wall sugars, acetyl bromide lignin and sugar release following saccharification by a cocktail of cellulases and xylanases, was assessed during plant development to full leaf senescence. These were determined in both individual internodes and in combined leaves and combined internodes of FAEA expressing and control partner plants.

Probing the role of cell wall feruloylation during maize development by differential expression of an apoplast targeted fungal ferulic acid esterase.

While many aspects of the growth of maize are well understood, the role of cell wall feruloylation particularly during internode elongation has not been firmly established, but results so far indicate that it has significant implications for both biofuel feedstock conversion and for crop yield. The growth of the cell wall is achieved by synthesis, integration and cross-linking between wall polymers. As ferulate oxidative coupling of arabinoxylan side chains constitutes a significant type of cross-link in grass cell walls, it is expected to have a crucial role in plant growth.

Reducing cell wall feruloylation by expression of a fungal ferulic acid esterase in Festuca arundinacea modifies plant growth, leaf morphology and the turnover of cell wall arabinoxylans.

A feature of cell wall arabinoxylan in grasses is the presence of ferulic acid which upon oxidative coupling by the action of peroxidases forms diferuloyl bridges between formerly separated arabinoxylans. Ferulate cross-linking is suspected of playing various roles in different plant processes. Here we investigate the role of cell wall feruloyaltion in two major processes, that of leaf growth and the turnover of cell wall arabinoxylans on leaf senescence in tall fescue using plants in which the level of cell wall ferulates has been reduced by targeted expression of the Aspergillus niger ferulic acid esterase A (FAEA) to the apoplast or Golgi.

Expression of a fungal ferulic acid esterase in suspension cultures of tall fescue () decreases cell wall feruloylation and increases rates of cell wall digestion.

In the cell walls of grasses ferulic acid is esterified to arabinosyl residues in arabinoxylans that can then undergo oxidative coupling reactions to form ferulate dehydrodimers, trimers and oligomers which function to cross-link cell-wall polysaccharides, limiting cell wall degradability. Fungal ferulic acid esterase can release both esterified monomeric and dimeric ferulic acids from these cell wall arabinoxylans making the cell wall more susceptible to further enzymatic attack and increasing cell wall degradability. Non-embryogenic cell suspension cultures of expressing a ferulic acid esterase () targeted to either the apoplast, or endoplasmic reticulum under the control of a constitutive actin promoter, or to the vacuole under the control of a soybean heat shock promoter, were established and FAE activity determined in the cells and medium during a growth cycle.

Functional testing of a PF02458 homologue of putative rice arabinoxylan feruloyl transferase genes in Brachypodium distachyon.

We show that changing the expression of a putative feruloyl transferase gene belonging to the BAHD acyl-transferase family alters the levels of cell wall esterified ferulates and diferulates in Brachypodium distachyon cell walls. While the potential of grass cell walls for biofuel production has been realized, the technology for lignocellulosic biomass conversion for the production of ethanol is still inefficient because of structural mechanisms that plants have evolved to make the cell wall recalcitrant to enzymatic attack. One of these mechanisms in grasses involves the esterification of arabinoxylans in the cell wall with ferulic acid via an ester linkage to arabinose side chains on xylans.