Xylem vessel‐specific SND5 and its homologs regulate secondary wall biosynthesis through activating secondary wall NAC binding elements

Abstract

Secondary cell wall biosynthesis has been shown to be regulated by a suite of transcription factors. Here, we identified a new xylem vessel-specific NAC domain transcription factor, secondary wall-associated NAC domain protein5 (SND5), in Arabidopsis thaliana and studied its role in regulating secondary wall biosynthesis.We showed that the expression of SND5 and its close homolog, SND4/ANAC075, was specifically associated with secondary wall-containing cells and dominant repression of their functions severely reduced secondary wall thickening in these cells. Overexpression of SND4/ 5 as well as their homologs SND2/3 fused with the activation domain of the viral protein VP16 led to ectopic secondary wall deposition in cells that are normally parenchymatous. SND2/3/ 4/5 regulated the expression of the same downstream target genes as do the secondary wall NAC master switches (SWNs) by binding to and activating the secondary wall NAC binding elements (SNBEs).Furthermore, we demonstrated that the poplar (Populus trichocarpa) orthologs of SND2/ 3/4/5 also activated SNBEs and regulated secondary wall biosynthesis during wood formation.Together, these findings indicate that SND2/3/4/5 and their poplar orthologs regulate the expression of secondary wall-associated genes through activating SNBEs and they are positioned at an upper level in the SWN-mediated transcriptional network.

A Phloem-Expressed PECTATE LYASE-LIKE Gene Promotes Cambium and Xylem Development

“…Ectopic lignification is one of the responses elicited by cell wall fragments during pathogen attack ( Ferrari et al, 2013 ), so lignification could have been a defence response activated by pectin fragments produced when PLL12 was overexpressed. However, closer examination of the dexamethasone-treated apices revealed cortex cells with lignification in a pitted pattern and openings between adjacent cells ( Figure 5I ), similar to root metaxylem and to ectopic metaxylem cells induced by the regulators of xylem differentiation, VND6 and SND5 ( Figures 5G–I ; Kubo et al, 2005 ; Zhong et al, 2021 ). Pitted cells were also seen within the vascular bundles of plants with a mild phenotype after PLL12 induction, but not in uninduced controls ( Supplementary Figure 5 ).…”

“…The most straightforward candidate signal would be OGs, although their developmental roles remain speculative ( Seifert and Blaukopf, 2010 ). Supporting a link to xylem differentiation, genes that respond early to OG treatment ( Moscatiello et al, 2006 ) included SND5 , which is part of the transcriptional network controlled by PXY ( Smit et al, 2020 ) and encodes a NAC domain protein that regulates secondary wall deposition in the xylem ( Zhong et al, 2021 ). However, indirect effects on other signalling pathways are also possible.…”

Integrated Transcriptomic and Proteomic Analysis in the Roadmap of the Xylem Development Stage in Populus tomentosa

“…Previous studies show that PtrWNDs directly binds to the SNBE sites present in the promoters of several of the WND-regulated TFs involved in secondary wall biosynthesis, cell wall modification, and PCD ( Zhong et al, 2021 ). MYB46 and MYB83 bind to the 7 bp SMRE, ACC(A/T)A(A/C)(T/C), and directly activate a series of TFs and secondary wall biosynthetic genes.…”

Spatio-Temporal Modification of Lignin Biosynthesis in Plants: A Promising Strategy for Lignocellulose Improvement and Lignin Valorization

“…For example, transgenic switchgrass plants with an overexpression of PvMYB4 had reduced lignin content and up to a 250% higher in biofuel production but at the same time were 40% shorter (Shen et al, 2012). Overexpression of SNDs genes, which belong to the MYB master switches known to regulate plant lignification and cell wall development, results in smaller rosettes with curly leaves in transgenic Arabidopsis (Zhong et al, 2011(Zhong et al, , 2021. These phenotypes could be the result of unforeseen metabolic plasticity, intrinsically variable transcriptional regulatory circuits, changes in spatio-temporal expression of genes, differences in cisregulatory element composition of genes or protein-protein interactions controlling their distinct tissue organization and patterning, cell wall formation, and growth architecture.…”