The value of Arabidopsis as a model for secondary xylem research

Secondary xylem (wood) is the most abundant lignocellulosic material used by mankind. Its differentiation is ensured by a tight mechanism that regulates the expression of thousands of genes. Our knowledge of the molecular mechanisms involved in secondary xylem formation has largely been extrapolated from studies performed using the basal part of the stem and/or the hypocotyl of the model plant Arabidopsis. We provide an illustrated structural description of the secondary xylem from the stem and hypocotyl of Arabidopsis and from the model tree Populus. Structural descriptions, supported by literature data and anatomical images, serve as the basis for comparing Arabidopsis 'woody' structures with the secondary xylem of Populus, thereby enabling a discussion of their usefulness in plant research. We also outline published research that used Arabidopsis to study the mechanisms of secondary xylem formation and discuss the challenges associated with this approach. Secondary xylem is a heterogeneous and difficult to analyse tissue. Our article addresses the missing gaps and provides insight into structural similarities/differences between the secondary xylem of Arabidopsis stem and hypocotyl and that of Populus. The goal was to make descriptions detailed yet accessible to plant scientists, including those who are not experts in anatomy.