NAC-MYB-based transcriptional regulation of secondary cell wall biosynthesis in land plants

Abstract

Plant cells biosynthesize primary cell walls (PCW) in all cells and produce secondary cell walls (SCWs) in specific cell types that conduct water and/or provide mechanical support, such as xylem vessels and fibers. The characteristic mechanical stiffness, chemical recalcitrance, and hydrophobic nature of SCWs result from the organization of SCW-specific biopolymers, i.e., highly ordered cellulose, hemicellulose, and lignin. Synthesis of these SCW-specific biopolymers requires SCW-specific enzymes that are regulated by SCW-specific transcription factors. In this review, we summarize our current knowledge of the transcriptional regulation of SCW formation in plant cells. Advances in research on SCW biosynthesis during the past decade have expanded our understanding of the transcriptional regulation of SCW formation, particularly the functions of the NAC and MYB transcription factors. Focusing on the NAC-MYB-based transcriptional network, we discuss the regulatory systems that evolved in land plants to modify the cell wall to serve as a key component of structures that conduct water and provide mechanical support.

A Key Role for Apoplastic H2O2 in Norway Spruce Phenolic Metabolism

“…Ten NAC genes were up-regulated during lignin formation, whereas six NAC genes were down-regulated (Supplemental Table S9). Similar observations were made for the R2R3-MYB transcription factor family, members of which act as second-level master regulators and/or direct regulators of secondary cell wall biosynthesis (Nakano et al, 2015;Zhong and Ye, 2015;Supplemental Table S9). In addition to NACs and MYBs, several members of the APETALA2/ethylene response element-binding protein (AP2/EREBP), LBD, WRKY, C2H2 zinc finger, and Tify transcription factor families showed up-regulation in lignin-forming conditions.…”

“…MYB and WRKY transcription factor families were enriched among the differentially expressed genes (Supplemental Table S9). NAC (NAM, ATAF1/2, and CUC2) transcription factors are important for secondary cell wall development in Arabidopsis (Nakano et al, 2015;Zhong and Ye, 2015) and are likely also involved in the regulation of secondary cell wall biosynthesis in conifers Raherison et al, 2015;Lamara et al, 2016). Ten NAC genes were up-regulated during lignin formation, whereas six NAC genes were down-regulated (Supplemental Table S9).…”

Plant Innate Immune Response: Qualitative and Quantitative Resistance

“…In addition, following pathogen invasion, more secondary metabolites are induced (RRI) and these form complex polymers that are deposited in xylem vessels to enforce cell walls (Gunnaiah et al, 2012;Wang et al, 2014b;Yogendra et al, 2015a). The conjugated complex metabolites, not degraded by the enzymes produced by most pathogens, are produced in the phenylpropanoid, flavonoid, fatty acid, and alkaloid metabolic pathways (Figure 2) (Nakano et al, 2015;Yogendra et al, 2015b). These play a significant role in plant resistance; Lignin: These are three-dimensional phenolic heteropolymers resulting from the oxidative coupling of three p-hydroxycinnamoyl (p-coumaryl, coniferyl, and sinapyl) alcohols.…”

“…The overexpression of VvWRKY1 induced a cinnamoyl alcohol dehydrogenase and a caffeic acid O-methyl transferase gene in grape vines, providing higher resistance to downy mildew (Marchive et al, 2013) and the transcriptional activation of StWRKY1 by heat shock protein (sHSP17.8)-induced phenylpropanoid genes in potato conferring resistance to late blight (Yogendra et al, 2015a). In plants, a battery of NAC and MYB TFs activate secondary cell wall formation based on lignin monomers (Nakano et al, 2015). WRKY29, a JA-responsive TF, was expressed only in F. graminearum-resistant genotype, Wangshuibai, but not when the QTL-Fhb1 region was deleted (Xiao et al, 2013).…”

“…The pathogens also try to neutralize the effect of these phytoalexins by converting them to less toxic oxidized forms or conjugate with glycosides through production of enzymes (Jeandet et al, 2014). Primary cell walls produced by cellulose and pectins are constitutively enforced by the deposition of secondary metabolites (RRC) (Bashline et al, 2014;Eudes et al, 2014;Nakano et al, 2015). In addition, following pathogen invasion, more secondary metabolites are induced (RRI) and these form complex polymers that are deposited in xylem vessels to enforce cell walls (Gunnaiah et al, 2012;Wang et al, 2014b;Yogendra et al, 2015a).…”