Metabolic Engineering
The metabolic engineering of primary metabolism provides an enormous potential to improve the value of plant-based raw materials for food and industrial applications. This chapter focuses on the current progress in the manipulation of carbohydrate and lip
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Metabolic Engineering Lars M. Voll and Frederik Bo¨rnke
11.1
Introduction
Quality traits, including alterations in metabolite composition of crop plants, have been major targets of traditional breeding programs. One of the most prominent examples is the introduction of rape seed varieties low in erucid acid (in seed oil) and in glucosinolates (in meal) approximately 30 years ago which was an important step towards improving the nutritional properties of rape seed products. However, conventional breeding strategies depend on the availability of significant genetic variation for a given trait within the species gene pool and are further limited by the complex genetics underlying some quality traits. Moreover, due to its untargeted nature breeding of novel traits is time-consuming and slow. The emergence of molecular biology and plant transformation technologies offers the possibility of manipulating plant metabolism by a more rapid, targeted approach. The widespread adoption of transgenic plants in the past two decades gave rise to the discipline of plant metabolic engineering and provided enormous progress concerning the manipulation of plant metabolism. Basically, metabolic engineering was defined as the alteration of metabolic output by the introduction of recombinant DNA (Bailey 1991) or, more specifically, as the genetic modification of cellular biochemistry to introduce new properties or to modify existing ones (Jacobsen and Khosla 1998). The main goals of plant metabolic engineering are to produce valuable compounds in an economically attractive format, or to increase yield of a crop plant. On the level of metabolites these goals can be achieved by: (i) an increase in the production of a specific desired compound, (ii) the deletion or reduction of a specific unwanted product and (iii) the introduction of pathways leading to new products. In contrast to conventional breeding, transgenic strategies offer a rapid way to introduce
L.M. Voll and F. Bo¨rnke Lehrstuhl fu¨r Biochemie, Friedrich-Alexander-Universita¨t Erlangen-Nu¨rnberg, Staudtstrasse 5, 91058 Erlangen, Germany e-mail: [email protected]; [email protected]
F. Kempken and C. Jung (eds.), Genetic Modification of Plants, Biotechnology in Agriculture and Forestry 64, DOI 10.1007/978-3-642-02391-0_11, # Springer-Verlag Berlin Heidelberg 2010
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desirable traits directly into the genome of elite varieties. It is clear, however, that the successful manipulation of plant metabolism requires detailed understanding of the underlying factors that regulate it. Traditionally, metabolic pathways have been analyzed on a step-by-step basis and limiting enzymes have been identified according to their biochemical properties or by using metabolic control analysis (ap Rees and Hill 1994; Geigenberger et al. 2004). Subsequently, enzyme overexpression is employed to alleviate metabolic bottlenecks. However, given the enormous flexibility of plant metabolism these direct approaches are often confounded by in
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