PtoMYB156 is involved in negative regulation of phenylpropanoid metabolism and secondary cell wall biosynthesis during wood formation in poplar

Li Yang,Lingyu Ran,Xin Zhao,Keming Luo,Chaofeng Li,Di Fan

doi:10.1038/srep41209

Abstract

Some R2R3 MYB transcription factors have been shown to be major regulators of phenylpropanoid biosynthetic pathway and impact secondary wall formation in plants. In this study, we describe the functional characterization of PtoMYB156, encoding a R2R3-MYB transcription factor, from Populus tomentosa. Expression pattern analysis showed that PtoMYB156 is widely expressed in all tissues examined, but predominantly in leaves and developing wood cells. PtoMYB156 localized to the nucleus and acted as a transcriptional repressor. Overexpression of PtoMYB156 in poplar repressed phenylpropanoid biosynthetic genes, leading to a reduction in the amounts of total phenolic and flavonoid compounds. Transgenic plants overexpressing PtoMYB156 also displayed a dramatic decrease in secondary wall thicknesses of xylem fibers and the content of cellulose, lignin and xylose compared with wild-type plants. Transcript accumulation of secondary wall biosynthetic genes was down-regulated by PtoMYB156 overexpression. Transcriptional activation assays revealed that PtoMYB156 was able to repress the promoter activities of poplar CESA17, C4H2 and GT43B. By contrast, knockout of PtoMYB156 by CRISPR/Cas9 in poplar resulted in ectopic deposition of lignin, xylan and cellulose during secondary cell wall formation. Taken together, these results show that PtoMYB156 may repress phenylpropanoid biosynthesis and negatively regulate secondary cell wall formation in poplar.

Highlights

In plants, phenylpropanoid compounds are a wide range of secondary metabolites including monolignols, flavonoids, stilbenes and various phenolic acids
Overexpression of PdMYB221 from P. deltoids led to a reduction in secondary cell wall thicknesses of fibers and vessels in transgenic Arabidopsis[34], indicating that PdMYB221 may be a repressor of secondary wall formation in poplar
Since PtoMYB156 shares significant similarity with other phenylpropanoid/lignin biosynthesis repressors such as AtMYB422, AmMYB30855, ZmMYB4225, ZmMYB3124 and ZmMYB1119, we investigated whether PtoMYB156 could negatively regulate the biosynthesis of phenylpropanoid compounds in transgenic plants

Summary

Introduction

Phenylpropanoid compounds are a wide range of secondary metabolites including monolignols, flavonoids, stilbenes and various phenolic acids. At least four MYB transcription factors (PtrMYB2, PtrMYB3, PtrMYB20 and PtrMYB21) have been demonstrated to be direct targets of PtrWNDs and functional orthologs of the Arabidopsis MYB46 and MYB83 which act as second-level master switches controlling secondary wall biosynthesis[4,14,15] These PtrMYBs are able to activate the promoter activities of poplar wood biosynthetic genes[15]. Other wood-associated transcription factors as master switches activated secondary wall biosynthesis during wood formation include the Eucalyptus EgMYB216 and the pine (Pinus taeda) PtMYB4/817,18 These transcription factors have been shown to be functional orthologs of Arabidopsis MYB46/83, and overexpression of PtMYB4 and EgMYB2 resulted in ectopic lignification in tobacco and Arabidopsis, respectively[13,17]. We demonstrated that PtoMYB156 functions as a transcriptional repressor and negatively regulates secondary cell wall formation in poplar

Methods

Results

Conclusion