Manipulating cellulose biosynthesis by expression of mutant A rabidopsis proM24::CESA3 ixr1‐2 gene in transgenic tobacco

Summary 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 CESA 3, AtCESA3 ixr1‐2 derived from A rabidopsis thaliana L . H eynh into a different plant family, the S olanceae dicotyledon tobacco ( N icotiana tabacum L . variety S amsun NN ). Specifically, a chimeric gene construct of CESA 3 ixr1‐2 , codon optimized for tobacco, was placed between the heterologous M24 promoter and the rbc SE 9 gene terminator. The results demonstrated that the tobacco plants expressing M 24‐ CESA 3 ixr1‐2 displayed isoxaben resistance, consistent with functionality of the mutated A t CESA 3 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 M 24‐ AtCESA3 ixr1‐2 caused aberrant spatial distribution of lignified secondary cell wall tissue and a reduction in the zone occupied by parenchyma cells.