Cell wall recalcitrance to cellulase digestibility is a key limitation to the use of plant cell walls in biofuel production. Pretreatments of biomass promote digestibility but are still inefficient. Extensins are structural cell wall proteins that are covalently crosslinked in plant cell walls. We are investigating whether extensins are removed by current biomass pretreatment protocols, and if not, whether pretreatment protocols can be altered to remove these proteins. We are testing pretreated biomass for the presence of hydroxyproline, a modified amino acid that is a major component of extensins. In addition, we are developing a reporter system in transgenic plants using fluorescently tagged extensin motifs to identify chemical and enzymatic treatments that are effective in releasing extensins from cell walls.