Genetic engineering of Pinus radiata and Picea abies, production of transgenic plants and gene expression studies

Abstract

ABSTRACT Plantation forestry, based on successful breeding of superior tree genotypes, is becoming more widely used by international forestry companies, since it offers the possibility to grow and manage forests of high economic value and superior quality. However, a number of highly desirable traits are not readily available in the breeding population and may be introduced using desirable genes from other organisms. Forest molecular biology, and in particular tree genetic engineering is now at a stage where the technologies are readily available to transfer specific traits of commercial and scientific interest into forest trees. Our efforts are aimed at the genetic engineering of plantation grown conifer trees such as Pinus radiata, Pinus taeda and Picea abies. Stable transformation technologies have been developed for embryogenic tissue using either Agrobacterium tumefaciens or a Biolistic® particle delivery system. Many genes from other organisms combined with promoters of various origins, were transferred into conifer tissue and transgenic plants recovered. Examples are genes for resistance against herbicides, genes involved in reproductive development, and genes involved in lignin formation. Analysis of transgenic tissue and plants has confirmed successful transfer of genes and their expression. For example, a herbicide resistance gene was introduced into Pinus radiata and Picea abies, and transgenic plants were regenerated and exposed to an operational concentration of the respective herbicide. Spray tests demonstrated the expression of the herbicide resistance gene and the newly acquired resistance of transgenic conifers to the herbicide. Another example is the expression of the endogenous cad gene in sense or antisense orientation in transgenic Pinus radiata tissue and plants. Biochemical analyses indicate that the influence of the inserted gene construct on the expression of the endogenous cad gene can be dependent on the developmental stage of the plant. A further challenge is provided by the growing numbers of potentially useful genes and promoter / gene combinations offering potential for forest trees. Early screening technologies that allow the quick and economic screening of candidate genes need to be developed to enable researchers to make the right choice of a gene for a specific purpose. To this end we are developing tissue culture protocols to produce secondary wall-forming cells and tracheary elements in vitro. These cells may be genetically transformed and may provide an excellent screening and gene expression analysis tool by avoiding the long periods of time otherwise necessary to regenerate and analyse transgenic plants.