A Molecular Blueprint of Lignin Repression

TLDR: This work provides a comprehensive overview of the molecular factors that negatively impact on the lignification process at both the transcriptional and post-transcriptional levels.

About: This article is published in Trends in Plant Science.The article was published on 2019-11-01 and is currently open access. It has received 20 citations till now. The article focuses on the topics: Lignocellulosic biomass.

Figures

Figure 2. PAL as a Case Study ofMultipleMechanisms Regulating Gene Expression and Protein Abundance. (A) PAL is directly repressed through binding of various TALE family transcription factors (TFs; e.g., BREVIPEDICELLUS) to the DNA knotted 1 (KN-1) motif, as well as by binding of subgroup 4 R2R3 MYBs (e.g., MYB4) to the AATAGTT motif. (B) PAL is indirectly regulated through BLH6–KNAT7-mediated repression of the HD-Zip III TF REVOLUTA. HB15 represses the expression of the master switches SND1 and NST2, which are activators of PAL expression. (C) Kelch F-box proteins ubiquitinate PAL to target it to the 26S proteasome for proteolysis. Other PAL regulatory pathways, including metabolic feedback repression (caffeic acid, cinnamic acid), environmental factors, and physical interactions with other phenylpropanoid enzymes (C4H) are beyond the scope of this figure but are reviewed in [44]. Abbreviations: BLH, BEL1-like homeodomain; HB, homeobox; KFB, kelch F-box; KNAT, knotted1-like TALE homeodomain; NST, NAC secondary wall thickening promoting factor; PAL, phenylalanine ammonia lyase; SND, secondary wall-associated NAC domain protein; Ub ubiquitin. This figure was created using BioRender (https://biorender.com/).

Table 1. Binding Sites of Proteins Involved in the Repression of Monolignol Biosynthesis

Figure 1. The repressive activity of EgMYB1 increases when it is associated with EgH1.3. Some factors are devoted to specifically preventing monolignol biosynthesis (blue boxes), whereas others repress secondary cell wall (SCW) formation more widely (violet boxes). Proteins repressing SCW formation are essentially involved in the spatiotemporal regulation of specific tissue development, such as preventing SCW deposition in pith (AtWRKY12, AtHB15) or restricting the timing and localization of xylem cell development (AtVNI2). Abbreviations: 4CL, 4-coumarate-CoA ligase; AldOMT, 5-hydroxyconiferaldehyde O-methyltransferase; ARK, arborknox; BLH, BEL1-like homeodomain; BP, brevipedicellus; C4H, cinnamate-4-hydroxylase; DRIF, divaricata and radialis interacting factor; H1.3, linker histone variant; hAT, hobo activator Tam3 transposase; HB, homeobox; KFB Kelch F-box; KNAT, knotted1-like TALE homeodomain; LAC, laccase; LTF, lignin biosynthesisassociated transcription factor; MED, Mediator; NST, NAC secondary wall thickening promoting factor; OFP, ovate family protein; P, phosphorylation; PAL, phenylalanine ammonia lyase; PCN, popcorona; SND, secondary wall-associated NAC domain protein; U, ubiquitin; VND vascular-related NAC domain; VNI, VND interacting; XND, xylem NAC domain. This figure was created using BioRender (https://biorender.com/).