Increasing fiber length and growth in transgenic tobacco plants overexpressing a gene encoding the Eucalyptus camaldulensis HD-Zip class II transcription factor

Since the woody plants are important bio-materials for paper, chemical and energy production, strategies for improvement of their properties are of considerable interest. We examined the expression of Eucalyptus camaldulensis transcription factor (TF) genes in xylem tissues using an oligo-microarray gene analysis technique. As a result, we isolated 21 TF genes related to xylem development. Following a functional investigation of 7 TFs in vitro, we selected the xylem TF gene EcHB1, which encodes a HD-Zip class II, for investigation as a transgene. EcHB1 expression was driven by the CaMV35S promoter in transgenic tobacco plants, which showed greater fiber length (≤20%) and plant height (≤50%) than wild-type plants. In addition, leaf, root and stem growth were significantly enhanced in the transgenic lines, which also had a lower acid-soluble lignin and hemicellulose content than wild-type. Our results indicate that metabolic flexibility might be involved in these improvements to xylem cell wall biosynthesis and that in addition to providing a growth advantage, such modifications may confer long-term structural integrity to the woody perennials.