Comparative Genomics of Cellulase Gene Families in the Grasses

Cellulases, or more specifically endo-(1,4)-β-glucanases, participate in cell wall metabolism in higher plants, including cellulose biosynthesis and degradation, modification of other wall polysaccharides that contain contiguous (1,4)-β-glucosyl residues, and wall loosening during cell elongation.  There are 23-29 individual genes in the cellulase gene families from barley, maize, sorghum, rice and Brachypodium, and phylogenetic analyses show clear differences in clade structure between the grasses and Arabidopsis.  Comparisons of gene structures and map positions have allowed orthologous genes in the five species to be identified and synteny between the grasses is found to be high.  Homoeologues resulting from ancient polyploidizations of the maize genome can also be identified. 

Transcript analyses indicate that certain members of the cellulase gene family are transcribed in many tissues, while others are transcribed with a more limited distribution.  There are strong correlations between transcript levels of several members of the cellulase family and the data suggest evolutionary conservation of co-expression patterns between orthologues across the grass family.  There are also strong correlations between certain members of the cellulase gene family and other genes known to be involved in cell wall loosening and cell expansion, such as expansins and xyloglucan endotransglycosylases.

The identification of these groups of genes now allow us to test hypotheses regarding their joint participation in wall synthesis, re-modelling and degradation, together with their potential role in lignocellulose conversion during biofuel production from specialist bioenergy grasses and cereal crop residues.