Carbohydrate Metabolism

Abstract

The yield from crop plants has been subject to improvement through conventional breeding and modifications in agricultural practice for many decades. More recently, the use of molecular genetic approaches has allowed more directed approaches towards crop improvement. Specific examples of both successful strategies and of fundamental knowledge gleaned from unsuccessful strategies are presented including manipulations of starch, sucrose and novel sugar content. The utility of metabolic control analysis in the identification of control points in metabolic pathway and its use in the prediction of changes in metabolite accumulation following enzyme modulation is discussed. Further examples of biotechnological manipulation focus on qualitative rather than quantitative aspects of carbohydrate metabolism detailing the introduction of novel pathways for synthesis, or functionalities, of polymers. Particular focus is given to fructan biosynthesis in non‐fructan accumulating species and the broad structural diversity of starch following genetic manipulation of the enzymes involved in its synthesis and degradation. Finally, the chapter concludes with an appraisal of the challenges that remain before the rational manipulation of carbohydrate becomes routine.

Mode of Inheritance of Primary Metabolic Traits in Tomato

“…This finding is of great importance with respect to attempts to breed crops with improved chemical composition, since many attempts to metabolically engineer plants to produce elevated levels of a given metabolite were able to meet this goal, but only at the cost of compromising yield (Fernie and Willmitzer, 2004;Van Camp, 2005). Evaluation of the trait network of the heterozygous ILHs revealed that morphological parameters were less tightly associated to metabolic traits than they were in the homozygous IL population and, furthermore, that while a minority of metabolites were clearly morphogically associated in both populations, the majority appeared to be linked only in the homozygous ILs.…”

“…However, it is only recently that these studies have largely focused on single, or at most, a handful, of metabolites, such as carotenoid content in tomato (Liu et al, 2003a), protein content in maize (Zea mays) (Moose et al, 2004), starch content in potato (Solanum tuberosum) and rice (Oryza sativa) (Fernie and Willmitzer, 2004), and tocopherol levels in Arabidopsis (Gilliland et al, 2006). Over the last few years, however, pathway-based approaches have began to be adopted.…”

Modulation of Fructokinase Activity of Potato (Solanum tuberosum) Results in Substantial Shifts in Tuber Metabolism

“…Whilst the role of FK has been the subject of intensive recent investigation in the closely related species tomato (Solanum lycopersicum; Kanayama et al 1997, Odanaka et al 2002, German et al 2003, the profound differences in metabolism in these species (see Fernie and Willmitzer 2004 for details) led us to address the role of FK in potato. For this purpose, we generated transgenic potato plants in two cultivars of potatoRecord and Desiree that expressed StFK1 in both the sense and antisense orientation.…”

Profiling of diurnal patterns of metabolite and transcript abundance in potato (Solanum tuberosum) leaves

“…Diurnal regulation of plant metabolism has been studied for many years with particular attention paid to carbohydrates such as sucrose and starch (Geiger and Servaites 1994;Kruger 1997;Fernie and Willmitzer 2004) and to important components of carbon-nitrogen interaction such as 2-oxoglutarate, glutamate and asparagine (Ferrario-Mery et al 2001;Stitt and Fernie 2003;Masclaux-Daubresse et al 2002). Important regulatory mechanisms such as the fructose 2, 6-bisphosphatemediated feedforward and feedback regulation of sucrose synthesis have been uncovered (see Stitt 1990;Winter and Huber 2000).…”