Current Understanding of the Genetics and Molecular Mechanisms Regulating Wood Formation in Plants

Abstract

Unlike herbaceous plants, woody plants undergo volumetric growth (a.k.a. secondary growth) through wood formation, during which the secondary xylem (i.e., wood) differentiates from the vascular cambium. Wood is the most abundant biomass on Earth and, by absorbing atmospheric carbon dioxide, functions as one of the largest carbon sinks. As a sustainable and eco-friendly energy source, lignocellulosic biomass can help address environmental pollution and the global climate crisis. Studies of Arabidopsis and poplar as model plants using various emerging research tools show that the formation and proliferation of the vascular cambium and the differentiation of xylem cells require the modulation of multiple signals, including plant hormones, transcription factors, and signaling peptides. In this review, we summarize the latest knowledge on the molecular mechanism of wood formation, one of the most important biological processes on Earth.

Keywords: biomass; secondary growth; vascular cambium; wood formation; xylem differentiation.

Figure 1

Wood formation in plants. (a) Simplified process of wood formation. Wood formation is initiated through cell divisions within the cylindrical vascular cambium layer, formed from the procambium. Then xylem cell differentiation, cell expansion, secondary cell wall (SCW) and pit formation, and programmed cell death (PCD) follow. Vascular cambium formation from procambium is shown in the stem cross-sections from below a tree: xylem (red), phloem (blue), and the cambium (yellow). (b) Stem cross-section and cell diagram for each stage of wood formation. The xylem is formed through the vascular cambium cell division and xylem cell differentiation, cell expansion, secondary cell wall formation and pit formation, and programmed cell death.

Figure 2

Molecular regulatory network of xylem cell formation. (a) Vascular cambium cell division and xylem cell differentiation. (b) Secondary cell wall formation, pit formation, and programmed cell death in xylem cell formation. Representative genes were depicted with hormones (blue). Genes with essential roles are described in the text.