Populus as a Model Tree

Model organisms are important in providing tractable experimental systems, tools, and resources to investigate conserved biological processes. Progress in understanding such processes in model organisms can, in many cases, then be used to inform the biology of other organisms closely or distantly related, thereby illuminating the nature of conserved processes as well as taxon-specific variations. Many aspects tree biology are difficult or impossible to study in herbaceous model plants, including a perennial habit and long life span, secondary growth from a vascular cambium, phenology including winter dormancy and re-activation of growth in spring, and mechanisms of adaptation to local environment over large geoclimatic ranges. For this reason, it has long been considered desirable to develop a model tree species. Trees of the genus Populus (poplars) are prominent forest tree species in temperate regions of the northern hemisphere and have been used as experimental organisms to understand various aspects of tree biology for over three decades. Rapid advances in generating genomic, bioinformatic, and functional genomic information and tools for poplars in the last 15–20 years, as well as specific aspects of poplar biology, have led to the widespread adoption of poplars as model tree. In this chapter, I review aspects of poplar biology that are relevant to its status a model tree, including some of the advantages and challenges in working with poplars compared to other plant model systems. I then briefly review the history of poplar as model tree, and touch upon on major advances in poplar genomics that have been crucial in its widespread recognition as a model tree species. Finally, I highlight some of the recent insights into selected biological processes important for tree biology gained from use of the poplar model system, such as secondary growth and wood formation, sexual maturation and seasonality, and adaptation to local environment.