Manipulating cellulose biosynthesis by expression of mutant ArabidopsisproM24:: CESA3^ixr1-2 gene in transgenic tobacco

Manipulation of the cellulose biosynthetic machinery in plants has the potential to provide insight into plant growth, morphogenesis and to create modified cellulose for anthropogenic use. Evidence exists that cellulose microfibril structure and its recalcitrance to enzymatic digestion can ameliorated via mis-sense mutation in the primary cell wall-specific gene AtCELLULOSE SYNTHASE (CESA)3. This mis-sense mutation has been identified based on conferring drug resistance to the cellulose inhibitory herbicide isoxaben. To examine whether it would be possible to introduce mutant CESA alleles via a transgenic approach, we overexpressed a modified version of CESA3, AtCESA3^ixr1-2 derived from Arabidopsis thaliana L. Heynh into a different plant family, the Solanceae dicotyledon tobacco (Nicotiana tabacum L. variety Samsun NN). Specifically, a chimeric gene construct of CESA3^ixr1-2, codon optimized for tobacco, was placed between the heterologous M24 promoter and the rbcSE9 gene terminator. The results demonstrated that the tobacco plants expressing M24-CESA3^ixr1-2 displayed isoxaben resistance, consistent with functionality of the mutated AtCESA3^ixr1-2 in tobacco. Secondly, during enzymatic saccharification, transgenic leaf- and stem-derived cellulose is 54%-66% and 40%-51% more efficient, respectively, compared to the wild type, illustrating translational potential of modified CESA loci. Moreover, the introduction of M24-AtCESA3^ixr1-2 caused aberrant spatial distribution of lignified secondary cell wall tissue and a reduction in the zone occupied by parenchyma cells.