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JXB Advance Access originally published online on March 12, 2007
Journal of Experimental Botany 2007 58(7):1761-1770; doi:10.1093/jxb/erm034
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© 2007 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.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

The glycine decarboxylase complex multienzyme family in Populus

Mohan Rajinikanth, Scott A. Harding and Chung-Jui Tsai*

Biotechnology Research Center, School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA

* To whom correspondence should be addressed. E-mail: chtsai{at}mtu.edu

In plants, the glycine decarboxylase complex (GDC) cooperates with serine hydroxymethyltransferase (SHMT) to mediate photorespiratory glycine–serine interconversion. GDC is also postulated to be an integral component of one-carbon (C1) metabolism in heterotrophic tissues, although molecular evidence in plants is scarce. An initial report of a xylem-specific isoform of GDC component H-protein, PtgdcH1, in aspen (Populus tremuloides Michx.) provided molecular evidence consistent with an important role for GDC in plant C1 metabolism. PtgdcH1 is phylogenetically distinct from the leaf-abundant photorespiratory PtgdcH3, but both isoforms restored GDC activity in a yeast H-protein knockout mutant, suggesting their functional equivalence. The Populus genome contains eight transcriptionally active GDC genes, encoding four H-proteins, two T-proteins, and single P- and L-proteins. The two Populus T-protein isoforms, PtgdcT1 and PtgdcT2, exhibited differential expression in leaves and xylem, similar to PtgdcH3 and PtgdcH1. In silico identification of AC elements in the promoters of xylem-abundant PtgdcH1 and PtgdcT2, as well as many lignin biosynthetic genes of Populus is consistent with a prominent role for GDC in methyl-intensive lignification during wood formation. The AC element is absent from Arabidopsis GDC promoters, and GDC expression has not been linked to secondary growth in this herbaceous annual. Taken together, the results suggest that the association of distinct H-protein and T-protein isoforms with photorespiration and C1 metabolism is a distinguishing feature of Populus, and may signify molecular adaptation of GDC to cope with the C1 demands of lignification in woody perennials.

Key words: One-carbon metabolism, lignin, photorespiration, Populus genome

Received 11 December 2006; Revised 1 February 2007 Accepted 5 February 2007


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