JXB Advance Access originally published online on February 16, 2008
Journal of Experimental Botany 2008 59(3):681-695; doi:10.1093/jxb/erm350
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© 2008 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Differential expression of three eucalyptus secondary cell wall-related cellulose synthase genes in response to tension stress
1Forest Biotechnology Group, Department of Forestry and Environmental Resources, College of Natural Resources, North Carolina State University, Raleigh, NC 27695, USA
2Biotechnology Research Center, School of Forest Resources and Environmental Sciences, Michigan Technological University, Houghton, MI 49931, USA
* To whom correspondence should be addressed. E-mail: slu{at}unity.ncsu.edu
Trees constitute the majority of lignocellulosic biomass existing on our planet. Trees also serve as important feedstock materials for various industrial products. However, little is known about the regulatory mechanisms of cellulose synthase (CesA) genes of trees. Here, the cloning and characterization of three CesA genes (EgraCesA1, EgraCesA2, and EgraCesA3) from an economically important tree species, Eucalyptus grandis, are reported. All three genes were specifically expressed in xylem cells of eucalyptus undergoing secondary cell wall biosynthesis. The GUS gene, expressed under the control of the EgraCesA2 or EgraCesA3 promoter, was also localized in the secondary xylem in transgenic tobacco stems. However, the EgraCesA1 promoter alone or along with its 5'-UTR introns was insufficient to direct appropriate GUS expression. EgraCesA2 and EgraCesA3 gene expression was up-regulated in tension-stressed eucalyptus xylem cells. Accordingly, GUS expression directed by the EgraCesA2 or EgraCesA3 promoter was also up-regulated. EgraCesA1 had no such response. Thus, it is most unlikely that EgraCesA1 is a subunit of the EgraCesA2–EgraCesA3 complex. The presence of at least two types of cellulose biosynthesis machinery in wood formation is an important clue in deciphering the underpinnings of the perennial growth of trees in various environmental conditions. By analysing GUS gene expression directed by the EgraCesA3 promoter or its deletions, several negative and positive regulatory regions controlling gene expression in xylem or phloem were identified. Also a region which is likely to contain mechanical stress-responsive elements was deduced. These results will guide further studies on identifying cis-regulatory elements directing CesA gene transcription and wood formation regulatory networks.
Key words: Cellulose, cellulose synthase, cell wall, Eucalyptus grandis, tension stress, wood formation
Present address: Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200032, China.
Present address: Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
Received 6 November 2007; Revised 4 December 2007 Accepted 12 December 2007