Polynucleotides, nucleic acid constructs, and methods are disclosed for the modification of cellulose and/or lignin content in plant tissues. Plants are genetically engineered with a gene encoding a C3HC4 protein, which leads to increased cellulose content when over-expressed in the plant vascular system. Plant transformants harboring the C3HC4 protein gene show increased content of cellulose and/or decreased lignin content, traits that are thought to improve hardwood trees for cellulose extraction during pulping and papermaking.