Regulation of secondary wall synthesis and cell death by NAC transcription factors in the monocot Brachypodium distachyon

Abstract

In several dicotyledonous species, NAC transcription factors act as master switches capable of turning on programmes of secondary cell-wall synthesis and cell death. This work used an oestradiol-inducible system to overexpress the NAC transcription factor BdSWN5 in the monocot model Brachypodium distachyon. This resulted in ectopic secondary cell-wall formation in both roots and shoots. Some of the genes upregulated in the process were a secondary cell-wall cellulose synthase (BdCESA4), a xylem-specific protease (BdXCP1) and an orthologue of AtMYB46 (BdMYB1). While activation of BdMYB1 may not be direct, this study showed that BdSWN5 is capable of transactivating the BdXCP1 promoter through two conserved binding sites. In the course of Brachypodium development, the BdXCP1 promoter was observed to be active in all types of differentiating tracheary elements. Together, these results suggest that Brachypodium SWNs can act as switches that turn on secondary cell-wall synthesis and programmed cell death.

The Dynamics of Transcript Abundance during Cellularization of Developing Barley Endosperm

“…One question of special relevance in the developing endosperm, where cell walls are not subject to secondary thickening, was whether TF repressors of secondary wall synthesis were expressed; many TFs that control secondary wall biosynthesis belong to the NAC or MYB groups (Zhou et al, 2009;Yao et al, 2012;Valdivia et al, 2013;Zhong and Ye, 2015;Zhou et al, 2014;Taylor-Teeples et al, 2015). Four putative MYB TFs and one NAC TF showed varied differential patterns across the 6 d time course.…”

Regulation of plant secondary metabolism and associated specialized cell development by MYBs and bHLHs

“…AtMYB46 and AtMYB83 together with their regulators, the secondary wall NAC transcription factors (SWNs), are functionally conserved in other angiosperm and gymnosperm species, including the SWN orthologs in Medicago , poplar, Eucalyptus , rice, maize and Brachypodium (Zhong et al, 2010a; Zhao et al, 2010; Zhong et al, 2011a; Zhong et al, 2011b; Valdivia et al, 2013), as well as the AtMYB46/83 orthologs in poplar, Eucalyptus and pine (Patzlaff et al, 2003a; Goichoechea et al, 2005; McCarthy et al, 2010; Zhong et al, 2010b; Zhong et al, 2013). By contrast, the AtMYB58/63 orthologs are present only in species within the rosid eudicot clade (Plant Genome Duplication Database; chibba.agtec.uga.edu/duplication/).…”

Navigating the transcriptional roadmap regulating plant secondary cell wall deposition

“…Functional orthologs of Arabidopsis SWNs and MYB46 have been experimentally verified in the monocots Brachypodium distachyon , Zea mays , and Oryza sativa , suggesting the establishment of the basic structure of the SCW transcriptional network at least prior to monocot-dicot divergence (Zhong et al, 2011a; Valdivia et al, 2013). Strong evidence also corroborates an Arabidopsis –like transcriptional cascade in woody angiosperm species.…”

“…The SNBE sequence is essential for SWN-mediated promoter activation, and cis -element copy number is correlated with the strength of promoter transactivation (Zhong et al, 2010c). Recently, SWN homologs in the monocot Brachypodium were also shown to recognise the SNBE (Valdivia et al, 2013). Wang et al (2011) have identified a significantly more specific SNBE-like element bound by SND1, TACNTTNNNNATGA, which does not appear to be semi-palindromic (Table 1).…”