Ectopic Expression of PtoMYB74 in Poplar and Arabidopsis Promotes Secondary Cell Wall Formation.

Chaofeng Li,Hong Yu,Keming Luo,Yongyao Fu,Xiaodong Ma

doi:10.3389/fpls.2018.01262

Abstract

In vascular plants, R2R3-MYB transcription factors are important regulators of secondary cell wall formation. Although 192 annotated R2R3 MYB genes were identified in the poplar genome, only a few members were characterized to participate in the regulation of the secondary cell wall biosynthesis. In this paper, we identify an R2R3-MYB transcription factor, PtoMYB74, which is predicted to be an ortholog of Arabidopsis AtMYB61, a transcription activator that regulates the secondary cell wall formation, lignin biosynthesis, stomatal aperture, and the mucilage of seed coat. PtoMYB74 is mainly expressed in the stems, especially in the xylem tissues and organs. PtoMYB74 as a transcriptional activator is localized to the nucleus. The overexpression of PtoMYB74 increased the secondary cell wall thickness of vessels in transgenic poplar and changed the secondary cell wall compositions. The expression levels of lignin and cellulose biosynthetic genes were elevated in the transgenic poplar overexpressing PtoMYB74 compared to the wild type, while there was no change in the xylan biosynthetic genes. Transcriptional activation assays demonstrated that PtoMYB74 could activate the promoters of structural genes in the lignin and cellulose biosynthetic pathways. Taken together, our data show that PtoMYB74 positively regulates the secondary cell wall biosynthesis in poplar.

Highlights

Wood, which is mainly composed of a secondary cell wall, is utilized for a wide range of applications, such as wood pulping, paper making, house construction, biofuels, and bio-functional coating (Pilate et al, 2004)
In Arabidopsis thaliana, genetic and molecular analyses have identified a number of NAC and MYB transcription factors involved in the secondary wall formation, and recently an NACMYB-mediated transcriptional network regulating the secondary cell wall formation has been constructed (Zhong and Ye, 2014)
The phylogenetic analysis revealed that PtoMYB74 had close relationships with PtMYB4, PtMYB8, HvMYB3, PtoMYB170, PtoMYB216, and AtMYB61 (Figure 1B), which are known to play important roles in the secondary cell wall formation (Wissenbach et al, 1993; Patzlaff et al, 2003; Bomal et al, 2008; Romano et al, 2012; Tian et al, 2013; Xu et al, 2017)

Summary

Introduction

Wood, which is mainly composed of a secondary cell wall, is utilized for a wide range of applications, such as wood pulping, paper making, house construction, biofuels, and bio-functional coating (Pilate et al, 2004). In Arabidopsis thaliana, genetic and molecular analyses have identified a number of NAC and MYB transcription factors involved in the secondary wall formation, and recently an NACMYB-mediated transcriptional network regulating the secondary cell wall formation has been constructed (Zhong and Ye, 2014). PtoMYB74 Regulates Secondary Wall Biosynthesis characterized as master switches that control many secondary wall-associated genes (Zhong et al, 2006; Mitsuda et al, 2007; Ohashi-Ito et al, 2010; Yamaguchi et al, 2011; Zhong and Ye, 2015) These NAC genes can directly or indirectly promote the expression of a great number of MYB genes (Zhong and Ye, 2015). Arabidopsis MYB26 is identified to up-regulate the expression of NST1 and NST2 genes (Yang et al, 2007; Ko et al, 2014)

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Results

Conclusion