Plant Cell Physiol-2010-McCarthy-1084-90

ThePoplarMYBTranscriptionFactors,PtrMYB3and

PtrMYB20, are Involved in the Regulation of Secondary Wall Biosynthesis

RyanL.McCarthy,RuiqinZhong,ScottFowler,DavidLyskowski,HasanthiPiyasena,KaraCarleton,CharlesSpicerandZheng-HuaYe

D epartment of Plant Biology, University of Georgia, Athens, GA 30602, USA Corresponding author: E-mail, zhye@plantbio.uga.edu ; Fax, + 1-706-542-1805

(Received March 28, 2010; Accepted April 23, 2010)

Short Communication

1084

Dicot wood is mainly composed of cellulose, xylan and lignin, and its formation requires the coordinated regulation of

their biosynthesis. In this report, we demonstrate that the poplar wood-associated MYB transcriptional activators, PtrMYB3 and PtrMYB20, activate the biosynthetic pathways of cellulose, xylan and linin when overexpressed in Arabidopsis and they are also able to activate the promoter activities of poplar wood biosynthetic genes. We also show that PtrMYB3 and PtrMYB20 are functional orthologs of

gArabidopsis MYB46 and MYB83, and their expression is

directly activated by poplar PtrWND2, suggesting their involvement in the regulation of wood formation in poplar. Keywords:Populus trichocarpa Secondarywall Transcriptionfactor Transcriptionalregulation.

Abbreviations:CaMV,cauli owermosaicvirus;GUS,βwallthickening -glucuronidase;NST,NACsecondarypromotingfactor;SND,secondarywall-associatedNACdomainprotein;VND,vascular-relatedNAC-domain.

Vascular plants are the primary sink of xed carbon dioxide on earth, and a large proportion of this xed carbon is stored as lignocellulosic polymers in plant cell walls. Lignocellulosic poly-mers are the principal components of wood, which represents the most abundant biomass produced by land plants. Because of the importance of wood in many industrial applications, such as pulping and paper-making, tremendous efforts have been put into understanding how lignocellulosic polymers in wood are synthesized in the hope of genetically engineering trees with altered wood composition. Recently, due to the potential of lignocellulosic polymers as a renewable source of biofuel production, study of wood formation has gained a renewed interest. To utilize lignocellulosic biomass ef ciently for biofuel production, it is imperative to have a complete picture of how individual polymers in wood are biosynthesized and how their biosynthesis is transcriptionally regulated. Uncovering the transcriptional regulators controlling wood

biosynthesis will probably provide novel tools to alter the bio-synthetic pathways of wood components based on our needs. Transcriptome pro ling of wood formation has identi ed a number of transcription factors that are preferentially expressed in developing wood. Some of these transcription factors show close homology to Arabidopsis meristem identity genes and were proposed to regulate the cambial activity ( Schrader et al. 2004 ), whereas others were suggested to mediate the regulation of the biosynthesis of lignocellulosic polymers in wood ( Bedon et al. 2007 , Wilkins et al. 2009 ). Due to the dif culty of genetic studies of gene functions in tree species, most of these wood-associated transcription factors have not yet been subjected to functional characterization. Among the few well-characterized transcription factors are several MYBs from pine (PtMYB1, PtMYB4 and PtMYB8) and

eucalyptus (EgMYB2). These pine and eucalyptus MYB genes have been shown to cause ectopic deposition of lignin or altered phenylpropanoid metabolism when overexpressed in tobacco or spruce ( Patzlaff et al. 2003 , Goicoechea et al. 2005 , Bomal et al. 2008 ). Because of their abilities to bind to the AC elements that are commonly present in the promoters of lignin biosyn-thetic genes, these pine and eucalyptus MYBs have been pro-posed to regulate lignin biosynthesis. However, it is not clear whether they also regulate the biosynthesis of other secondary wall components during wood formation.

PtMYB4 and EgMYB2 are phylogenetically closely related

to Arabidopsis MYB46 and MYB83 ( Fig. 1A ), which are direct targets of a group of NAC domain master regulators, including SND1, NST1, NST2, VND6 and VND7, controlling secondary wall biosynthesis in Arabidopsis ( Kubo et al. 2005 , Mitsuda et al. 2005 , Zhong et al. 2006 , Mitsuda et al. 2007 , Zhong et al. 2007b , Zhou et al. 2009 ). MYB46 and MYB83 have been shown to be another level of key switches capable of activating the entire secondary wall biosynthetic program and they function redun-dantly in regulating the secondary wall biosynthesis in bers and vessels ( Zhong et al. 2007a , McCarthy et al. 2009 ). In this report, we demonstrate that the poplar wood-associated MYB

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Plant Cell Physiol. 51(6): 1084–1090 (2010) doi:10.1093/pcp/pcq064, available online at doc.guandang.net; The Author 2010. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Plant Cell Physiol. 51(6): 1084–1090 (2010) doi:10.1093/pcp/pcq064 © The Author 2010.