Lignin biosynthesis and accumulation in response to abiotic stresses in woody plants

Woody plants have to experience various abiotic stresses due to their immobility and perennial characteristics. However, woody plants have evolved a series of specific regulation pathways in physiological and molecular mechanisms to deal with adverse environments. Compared with herbaceous plants, perennial woody plants have the advantages of developed roots and hard stems, and increased secondary xylem, which can strengthen the vascular system of the plants. The lignification process involves the lignin deposition on the cell wall by oxidation and polymerization of lignin monomer, which plays an important role in abiotic stress tolerance. This review focuses on recent progress in the biosynthesis, content, and accumulation of lignin in response to various abiotic stresses in plants. The role of transcription factors is also discussed in regulating lignin biosynthesis to enhance abiotic stress tolerance via changing cell wall lignification. Although woody plants shared similar lignin biosynthesis mechanisms with herbaceous plants, the temporal and spatial expression and stress response profiles of lignin biosynthetic genes provide the basis for the differences in stress tolerance of various species. An in-depth understanding of the role of lignin in the abiotic stress tolerance of woody plants will lay the foundation for the next step in tree resistance breeding through genetic engineering.