Plant Cell Walls: From the Plant to Human Health and Renewable Biofuels

Functional genomics technologies have accelerated the identification of genes involved in molecular and cellular processes that underpin the synthesis, re-modelling and degradation of cell walls in higher plants.  In the case of cellulose biosynthesis, it is now possible to follow the movement of the synthetic complex through the plasma membrane in real time.  However, identification of genes mediating the biosynthesis of some of the major wall polysaccharides remains elusive and devising rigorous proof-of-function for candidate genes can be equally challenging.  For example, the genes that mediate the biosynthesis of heteroxylans, which are found in walls of most plants and are particularly abundant in walls of the grasses, have not been characterized.     

New high throughput technologies have also been used to define changes that occur during fungal infection of plants.  Given that cell wall – cell wall contact is usually an early event in plant-pathogen interactions, it is not surprising that wall compositions of both the fungus and the host plant are important determinants of the success or otherwise of the pathogen’s attack on the plant, or that changes in wall properties in response to this initial contact will similarly contribute to the interaction.   

Advances in fundamental information on the genetics, cell biology and biochemistry of plant cell wall biology are now being applied in the emerging areas of renewable biofuel production and improved human health.  Thus, plant cell walls represent the world’s largest renewable carbon resource and are targets for manipulation to enhance conversion yields during bioethanol production.  The non-cellulosic polysaccharides of walls are not digested by human small intestinal enzymes and therefore contribute to total dietary fibre intake in human diets.  Through their defining impact on the bacterial population of the large intestine, the non-cellulosic wall polysaccharides are becoming recognized for their potential to lower the risk of serious human health conditions such as type II diabetes, cardiovascular disease, colorectal cancer and diverticular disease.

Attempts to manipulate levels of wall polysaccharides to address these health and biofuels objectives have been successful in some cases, but our ability to manipulate certain ‘core’ components of the wall can lead to severe phenotypic changes. 

many of the   are still being defined.  We have particularly focused on cell wall biology and biochemistry in the grasses, which arguably include the most important plants for human nutrition.  Foods derived from rice, wheat, maize, sorghum, barley, millets and sugar cane account for a high proportion of global caloric intake.  Forage and fodder grasses support the production of domesticated livestock, while switchgrass, Miscanthus spp. and other perennial grasses show great promise as biomass energy crops.