Genetic Transformation in Liriodendron tulipifera L. (Yellow Poplar)
Liriodendron tulipifera L. (yellow poplar) is one of the most common hardwood forest species in eastern North America, growing throughout the eastern United States and into southern Ontario, Canada. The species is most abundant and reaches its largest siz
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1 Introduction 1.1 Distribution and Importance of Liriodendron tulipifera Liriodendron tulipifera L. (yellow poplar) is one of the most common hardwood forest species in eastern North America, growing throughout the eastern Uni ted States and into southern Ontario, Canada. The species is most abundant and reaches its largest size in the lower Ohio River valley and in the Appalachian mountains ofNorth Carolina, Tennessee, Kentucky, and West Virginia (Fowells 1965). Although it is an early-stage successional species on most sites, the rapid growth rate of yellow poplar and the large size of mature trees (up to 60 m) make it a dominant canopy species. These growth characteristics, along with its straight form, self-pruning ability, and wood ofhighly desirable working quality (Wilcox and Taft 1969), make yellow poplar a valuable timber species. It has been employed for furniture (mostly hidden parts), plywood, corestock, millwork, siding, and other light construction lumber. It is also used for such gluewood products as chip board, ftakeboard, and oriented strandboard. Breeding pro grams have been established to take advantage of genetic variation in characteristics such as height growth (Farmer et al. 1983) and wood-specific gravity (Thorbjornsen 1961; Wilcox and Taft 1969). Bees are a primary pollinator of yellow poplar, and the species is known as a good honey producer. Yellow poplar is widely planted as an ornamentallandscape tree, admired for its symmetricalleaves and yellow, green, and orange ftowers. A number ofhorticultural cultivars have been described for the species (Santamour and McArdle 1984; see also Merkle and Sommer 1991 for more details).
1.2 Need for Transformation A gene transfer system for yellow poplar is required for two lines of research involving this species: (1) the development of trees for environmental remediation, and (2) a molecular genetic analysis of regeneration. Because of its wide I Environmental Research Laboratory, U.S. Environmental Protection Agency, 960 College Station Rd., Athens, Georgia 30613, USA 2 Daniel B. WarneIl School ofForest Resources, University ofGeorgia, Athens, Georgia 30605, USA
Biotechnology in Agriculture and Forestry, Vol. 29 Plant Protoplasts and Genetic Engineering V (ed. by Y.P.S. Bajaj) Springer-Verlag Berlin Heidelberg 1994
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H.D. Wilde and S.A. Merkle
range, fast growth rate, and efficient regeneration, it is a suitable candidate for the development of a forest tree capable ofheavy metal detoxification. This trait could be introduced into yellow poplar with the transfer of a bacterial gene which encodes an enzyme that detoxifies ionic mercury. The transfer ofthis gene, merA, has been found to transmit the capability for metal ion reduction to a eukaryotic organism (Saccharomyces cerevisiae; Rensing et al. 1992). The merA gene is currently being modified for expression in plants. Yellow poplar also has potential as a model system for tree developmental biology because of its embryogenic capacity (Merkle et al. 1993), small genome size (IN = 0.
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