Two NAC domain transcription factors, SND1 and NST1,

Planta (2007) 225:1603–1611

DOI 10.1007/s00425-007-0498-y

RAPID COMMUNICATION

Two NAC domain transcription factors, SND1 and NST1, function redundantly in regulation of secondary wall synthesis in W bers of Arabidopsis

Ruiqin Zhong · Elizabeth A. Richardson ·

Zheng-Hua Ye

Received: 12 December 2006 / Accepted: 9 February 2007/ Published online: 1 March 2007

© Springer-Verlag 2007

Abstract Secondary walls are the major component of wood, and studies of the mechanisms regulating sec-ondary wall synthesis is important for understanding the process of wood formation. We have previously shown that the NAC domain transcription factor SEC-ONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) is a key regulator of secondary wall synthesis in W bers of Arabidopsis thaliana stems and dominant repression of SND1 leads to a reduction in secondary wall thickening in W bers. However, T-DNA knockout of the SND1 gene did not cause an alteration in secondary wall thickness, suggesting that other SND1 homologs may compensate for the loss of SND1 expression. Here, we studied the e V ects of simultaneous inhibition of SND1 and its homolog, NAC SECONDARY WALL THICKENING PRO-MOTING FACTOR1 (NST1), on secondary wall syn-thesis in W bers. We show that simultaneous RNA interference (RNAi) inhibition of the expression of both SND1 and NST1 genes results in loss of secondary wall formation in W bers of stems. The W ber cells in the stems of SND1/NST1–RNAi plants lack all three major secondary wall components, including cellulose, xylan, and lignin, which is accompanied by a severe reduction in the expression of genes involved in their biosynthe-sis. In addition, inhibition of SND1 and NST1 leads to down-regulation of several W ber-associated transcrip-tion factor genes. Double T-DNA knockout mutations of SND1 and NST1 genes cause the same e V ects, as does simultaneous RNAi inhibition of SND1 and NST1. Our results provide W rst line evidence demon-strating that SND1 and NST1 function redundantly in the regulation of secondary wall synthesis in W bers.

Keywords Arabidopsis thaliana · Fiber cell · NAC domain transcription factor · Secondary wall synthesis · Transcriptional regulation

Abbreviations

NST NAC secondary wall thickening promoting factor

SND secondary wall-associated NAC domain

protein

VND vascular-related NAC domain

Introduction

Evolution of the ability to produce secondary walls was a pivotal step for vascular plants to dominate the ter-restrial habitats. It enabled vascular plants to form strong thick-walled cells for water transport and mechanical support (Raven et al. 1999). In tree species, secondary wall-containing cells, tracheary elements and/or W bers, are the main constituents of wood, which is widely used for pulping, papermaking, and many other commodities. Understanding the regulatory mechanisms controlling secondary wall formation is an important issue in plant biology and has signi W cant implications in tree biotechnology.

Secondary walls are deposited inside the primary walls after cells cease to elongate. To make secondary walls, genes involved in the biosynthesis of secondary wall components, including cellulose, hemicellulose

R. Zhong · E. A. Richardson · Z.-H. Ye (&) Department of Plant Biology,

University of Georgia,

Athens, GA 30602, USA

e-mail: zhye@