EgMYB1, an R2R3 MYB transcription factor from eucalyptus negatively regulates secondary cell wall formation in Arabidopsis and poplar

Abstract

Summary• The eucalyptus R2R3 transcription factor, EgMYB1 contains an active repressor motif in the regulatory domain of the predicted protein. It is preferentially expressed in differentiating xylem and is capable of repressing the transcription of two key lignin genes in vivo.• In order to investigate in planta the role of this putative transcriptional repressor of the lignin biosynthetic pathway, we overexpressed the EgMYB1 gene in Arabidopsis and poplar.• Expression of EgMYB1 produced similar phenotypes in both species, with stronger effects in transgenic Arabidopsis plants than in poplar. Vascular development was altered in overexpressors showing fewer lignified fibres (in phloem and interfascicular zones in poplar and Arabidopsis, respectively) and reduced secondary wall thickening. Klason lignin content was moderately but significantly reduced in both species. Decreased transcript accumulation was observed for genes involved in the biosynthesis of lignins, cellulose and xylan, the three main polymers of secondary cell walls. Transcriptomic profiles of transgenic poplars were reminiscent of those reported when lignin biosynthetic genes are disrupted.• Together, these results strongly suggest that EgMYB1 is a repressor of secondary wall formation and provide new opportunities to dissect the transcriptional regulation of secondary wall biosynthesis.

Natural Hypolignification Is Associated with Extensive Oligolignol Accumulation in Flax Stems

“…In contrast, no orthologs corresponding to the MYB factors AtMYB58 or AtMYB63 directly implicated in the regulation of lignin biosynthesis (Zhou et al, 2009) were differentially regulated. We also identified a MYB TF transcript that was significantly more abundant in stem outer tissues and belongs to subgroup 4, which includes repressors of the lignin biosynthetic pathway such as AtMYB4, EgMYB1, and ZmMYB31/42 (Jin et al, 2000;Fornalé et al, 2006Fornalé et al, , 2010Legay et al, 2010). Although functional analyses are obviously necessary, the expression of a potential lignin repressor in outer tissues is consistent with the hypolignified nature of this tissue.…”

A comparative transcriptomic approach to understanding the formation of cork

“…Statistical significance was calculated with Student's t test (*P < 0.05; **P < 0.01) precursors of other compounds such as flavonoids, and so a greater accumulation of these compounds in cork cannot be ruled out. Interestingly, the putative ortholog of Arabidopsis AtMYB4 or Eucalyptus EgMYB1, a well-known repressor of the phenylpropanoid metabolism and lignin biosynthesis (Jin et al 2000;Legay et al 2010), is strongly downregulated in cork. The downregulation of this repressor gene in cork oak agrees with the upregulation of phenylpropanoid biosynthetic enzymes such as PAL, C4H and 4CL in the same tissue, similarly as Cavallini et al (2015) found in petunia petals overexpressing MYB4.…”

The MYB182 Protein Down-Regulates Proanthocyanidin and Anthocyanin Biosynthesis in Poplar by Repressing Both Structural and Regulatory Flavonoid Genes

“…1A). In the lignin or phenylpropanoid repressor MYBs such as AtMYB4 and Eucalyptus gunnii EgMYB1 (Jin et al, 2000;Legay et al, 2010), a zinc-finger motif (CX1-2CX7-12CX2C) and a C4 motif (FLGLx4-7V⁄LLD⁄GF⁄YR⁄Sx1LEMK) were present. These motifs were not found in FaMYB1, VvMYBC2-L1, PhMYB27, and the new poplar MYBs.…”