Genetic modification of amino acid metabolism in woody plants

Forest trees comprise a large group of angiosperm and gymnosperm species of economic importance that play a crucial role in the ecosystems. Nitrogen is frequently a limiting factor for growth of forest trees, thus development of a fundamental understanding of nitrogen assimilation and metabolism is particularly important in broadening our understanding of fundamental tree biology. There are a number of fundamental ways in which woody plants differ from herbaceous species, including seed dormancy and germination, growth habit and enhanced secondary development, management of reduced nitrogen during dormancy, and the metabolic requirements for secondary growth, a major sink for both reduced nitrogen and carbon. Poplar species (Populus spp.) have emerged as model systems for research in woody angiosperms. Modification of metabolism using genetic engineering approaches has recently focussed on altering the biosynthesis of glutamine, polyamines, glutathione, and lignin. These approaches potentially affect plant development and stress tolerance. The aim of this minireview is to integrate the experimental genetic engineering approaches in the context of developing an increased understanding of overall nitrogen and amino acid metabolism in trees.