Lignin is one of the major factors in determining the woodiness of plants. Although wood and fibre formation are characteristic of trees, many herbaceous species including the model plant Arabidopsis thaliana develop stems with secondarily thickened cell walls rich in lignin that provide mechanical support during flowering. BLADE-ON-PETIOLEs are transcription factors in Arabidopsis that regulate plant architecture through modulation of growth and meristem activity. Members of this family have a transcriptional activation domain but lack a DNA-binding domain and require TGA-binding basic
leucine zipper (bZIP) as co-factors for recruitment to DNA. Arabidopsis plants that overexpress BOPs are late-flowering with short internodes containing excessive lignin. Poplar tree has a pair of BOP-like genes, but their role in tree development is unknown. Comparison of BOP function in Arabidopsis and poplar can lead to a better understanding of developmental regulation of lignin biosynthesis in plants.