How endogenous plant cell-wall degradation mechanisms can help achieve higher efficiency in saccharification of biomass.
Cell-wall recalcitrance to hydrolysis still represents one of the major bottlenecks for second-generation bioethanol production. This occurs despite the development of pre-treatments, the prospect of new enzymes, and the production of transgenic plants with less-recalcitrant cell walls. Recalcitrance, which is the intrinsic resistance to breakdown imposed by polymer assembly, is the result of inherent limitations in its three domains. These consist of: (i) porosity, associated with a pectin matrix impairing trafficking through the wall; (ii) the glycomic code, which refers to the fine-structural emergent complexity of cell-wall polymers that are unique to cells, tissues, and species; and (iii) cellulose crystallinity, which refers to the organization in micro- and/or macrofibrils. One way to circumvent recalcitrance could be by following cell-wall hydrolysis strategies underlying plant endogenous mechanisms that are optimized to precisely modify cell walls in planta. Thus, the cell-wall degradation that occurs during fruit ripening, abscission, storage cell-wall mobilization, and aerenchyma formation are reviewed in order to highlight how plants deal with recalcitrance and which are the routes to couple prospective enzymes and cocktail designs with cell-wall features. The manipulation of key enzyme levels in planta can help achieving biologically pre-treated walls (i.e. less recalcitrant) before plants are harvested for bioethanol production. This may be helpful in decreasing the costs associated with producing bioethanol from biomass.
Laboratory of Plant Physiological Ecology (LAFIECO), Department of Botany, Institute of Biosciences, University of São Paulo, Rua do Matão 277, São Paulo, SP, Brazil.
Eveline Q P
EQ
Tavares
Laboratory of Plant Physiological Ecology (LAFIECO), Department of Botany, Institute of Biosciences, University of São Paulo, Rua do Matão 277, São Paulo, SP, Brazil.
Amanda P
AP
De Souza
Laboratory of Plant Physiological Ecology (LAFIECO), Department of Botany, Institute of Biosciences, University of São Paulo, Rua do Matão 277, São Paulo, SP, Brazil msbuck@usp.br.
Marcos S
MS
Buckeridge
D018533:Biomass; D050260:Carbohydrate Metabolism; D002473:Cell Wall / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*
Abscission; aerenchyma; bioenergy; cell wall; cell-wall polysaccharide; fruit ripening; pre-treatment; recalcitrance storage mobilization.