Recent Advances in the Transcriptional Regulation of Secondary Cell Wall Biosynthesis in the Woody Plants

Abstract

Plant cell walls provide structural support for growth and serve as a barrier for pathogen attack. Plant cell walls are also a source of renewable biomass for conversion to biofuels and bioproducts. Understanding plant cell wall biosynthesis and its regulation is of critical importance for the genetic modification of plant feedstocks for cost-effective biofuels and bioproducts conversion and production. Great progress has been made in identifying enzymes involved in plant cell wall biosynthesis, and in Arabidopsis it is generally recognized that the regulation of genes encoding these enzymes is under a transcriptional regulatory network with coherent feedforward and feedback loops. However, less is known about the transcriptional regulation of plant secondary cell wall (SCW) biosynthesis in woody species despite of its high relevance to biofuels and bioproducts conversion and production. In this article, we synthesize recent progress on the transcriptional regulation of SCW biosynthesis in Arabidopsis and contrast to what is known in woody species. Furthermore, we evaluate progress in related emerging regulatory machineries targeting transcription factors in this complex regulatory network of SCW biosynthesis.

Marginal Lands to Grow Novel Bio-Based Crops: A Plant Breeding Perspective

“…However, the relative abundance, composition, and structure of cell wall components vary extensively across species, tissues and developmental stages (Vogel, 2008;Sarkar et al, 2009;Loque et al, 2015). Likewise, the occurrence and functionality of major cell wall synthetic genes is also conserved across plants (e.g., CESAs and CSLs as main players of cellulose and hemicellulose biosynthesis, respectively) (Vogel, 2008;Xu et al, 2009;Zhang et al, 2018), even if inter-specific differences exist also at the genetic level, which affect cell wall composition (e.g., the presence of CSL-Fs and CSL-Hs only in certain plant clades, which synthesize mixed-linkage glucans) (Vogel, 2008;Doblin et al, 2009). Taken together, these observations point out a large margin for the improvement of cell wall composition toward low-recalcitrant and purpose-made cell wall ideotypes.…”

A Molecular Blueprint of Lignin Repression

“…The roles of transcriptional activators promoting lignin biosynthesis have been well documented in various plants, such as thale cress (Arabidopsis thaliana) (reviewed in [12]) and tree species (reviewed in [13,14]). The negative regulators of lignin biosynthesis and their underlying directing networks are tightly controlled.…”

KNAT2/6b, a class I KNOX gene, impedes xylem differentiation by regulating NAC domain transcription factors in poplar

“…S10), a negative regulator of xylem differentiation, was significantly elevated in OE-5 and OE-7 plants (Fig. We also identified DEGs involved in wood formation Zhang et al, 2018) (Table S4). We also identified DEGs involved in wood formation Zhang et al, 2018) (Table S4).…”

“…S9). Among all DEGs, NAC and MYB genes related to xylem differentiation and secondary wall regulation Zhang et al, 2018), such as (Table S3). The downregulation of DEGs related to xylem differentiation, secondary wall regulation and synthesis was consistent with the repressed xylem differentiation and secondary wall formation observed in PagKNAT2/6b OE plants.…”

“…Wood development goes through primary growth, during which the shoot apical meristem (SAM) and root apical meristem (RAM) differentiate into the shoot and root, and continues to secondary growth, during which vascular cambial initials divide and differentiate into xylem and phloem cells with thickened secondary cell walls (Groover & Robischon, 2006;Baucher et al, 2007). After decades of efforts, largely based on studies of Arabidopsis, the regulatory factors affecting cambial cell maintenance, xylem and phloem differentiation, secondary wall synthesis, and programmed cell death have been identified, and the regulatory network underlying wood formation has been preliminarily proposed Zhang et al, 2018). NAM/ATAF/CUC (NAC) domain proteins may act as master regulators of xylem differentiation and secondary wall formation.…”