MYB58 and MYB63 Are Transcriptional Activators of the Lignin Biosynthetic Pathway during Secondary Cell Wall Formation in Arabidopsis    

Abstract

It has previously been shown that SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) is a key transcription factor regulating secondary cell wall formation, including the biosynthesis of cellulose, xylan, and lignin. In this study, we show that two closely related SND1-regulated MYB transcription factors, MYB58 and MYB63, are transcriptional regulators specifically activating lignin biosynthetic genes during secondary wall formation in Arabidopsis thaliana. MYB58 and MYB63 are phylogenetically distinct from previously characterized MYBs shown to be associated with secondary wall formation or phenylpropanoid metabolism. Expression studies showed that MYB58 and MYB63 are specifically expressed in fibers and vessels undergoing secondary wall thickening. Dominant repression of their functions led to a reduction in secondary wall thickening and lignin content. Overexpression of MYB58 and MYB63 resulted in specific activation of lignin biosynthetic genes and concomitant ectopic deposition of lignin in cells that are normally unlignified. MYB58 was able to activate directly the expression of lignin biosynthetic genes and a secondary wall-associated laccase (LAC4) gene. Furthermore, the expression of MYB58 and MYB63 was shown to be regulated by the SND1 close homologs NST1, NST2, VND6, and VND7 and their downstream target MYB46. Together, our results indicate that MYB58 and MYB63 are specific transcriptional activators of lignin biosynthesis in the SND1-mediated transcriptional network regulating secondary wall formation.

A Key Role for Apoplastic H2O2 in Norway Spruce Phenolic Metabolism

“…In Arabidopsis, AtMYB58 and AtMYB63 directly activate lignin biosynthesis genes by binding to AC elements present in the promoters of most of the genes in the phenylpropanoid and monolignol pathways (Zhou et al, 2009). A few putative spruce MYB genes (MA_10430220g0010, MA_1201g0010, and MA_137934g0010) with similarity to these Arabidopsis MYB genes showed significant up-regulation during lignin formation.…”

MYB transcription factor genes as regulators for plant responses: an overview

“…AtMYB58, AtMYB63 and AtMYB85 activated lignin biosynthesis in fibers and/or vessels (Zhou et al 2009). AtMYB46 is found to be a positive regulator of lignin biosynthesis in fibers and vessels and also regulated cellulose and xylan deposition (Zhong et al 2007).…”

Systematic Identification of Functional Plant Modules through the Integration of Complementary Data Sources

“…6A), is derived from the GO term "chitin metabolic process" and also includes some PPIs, TF targets, and AraNet edges. The module contains five true-positive genes, MYB DOMAIN PROTEIN63 (MYB63; Zhou et al, 2009), IRREGULAR XYLEM15 (IRX15) and IRX15-L (Brown et al, 2011), NAC DOMAIN CONTAINING PROTEIN73 (ANAC073) (Zhong et al, 2008), and REDUCED WALL ACETYLATION1 (RWA1) (Lee et al, 2011), all of which were correctly predicted to be involved in cell wall biogenesis. MYB63 and ANAC073 are a MYB and a NAC TF, respectively, and whereas MYB63 was known to be involved in JA/SA response pathways (Yanhui et al, e Genes that were present in both conserved and nonconserved modules could gain a prediction by both.…”