Genetic Engineering for Secondary Xylem Modification: Unraveling the Genetic Regulation of Wood Formation

Wood is produced by the successive addition of the secondary xylem, which differentiates from the vascular cambium. The secondary cell wall is a key feature of the secondary xylem, providing structural integrity to the plant and serving as one of the most important renewable resources on the planet. Understanding the genetic regulation of this complex biosynthetic process has been elusive, but recent advances in biotechnology and the development of model systems have yielded great insights into coordinated regulation of the growth and differentiation of the vascular cambium, leading to the production of woody biomass. As secondary walls represent the vast majority of woody biomass, genetic regulation of the biosynthesis of secondary walls has been gaining research interest in recent years. Genes encoding secondary wall-associated cellulose synthases and enzymes involved in lignin and hemicellulose synthesis have been identified. Furthermore, many transcriptional regulators of secondary wall biosynthesis have been discovered, including transcription factor MYB46 and its paralogue MYB83 that serve as master regulators of the secondary wall biosynthesis network. This growing understanding of the regulation of these processes could result in genetically designed planting stock that will not only support existing industries, but also lead to the sustainable development of new industries based on cellulose nanocrystals, wood-derived composites, and biofuels. However, any attempt to regulate cell wall composition must be carried out in the context of whole plant physiology, given the fundamental role that secondary wall formation plays in the growth and development of vascular plants.