Introduction

There is a continued need for agriculture to reinvent itself, striving towards enhanced productivity, cost-efficiency, and crop quality. Farmers employ increasingly complex crop management systems and eagerly adopt new varieties that promise higher yields. Such varieties need to display a combination of exceptional traits that protect against a multitude of stresses, ensure crop uniformity and storability, and are demanded by consumers. Plant breeders attempt to combine these traits by using methods that rely on random genome modifications such as double-bridge crosses, somatic hybridization, chemical mutagenesis, and g-radiation. However, such methods are often too imprecise to remove unwanted plant characteristics while they can also substantially compromise the integrity of genomes (Rommens 2008). They can also result in obscure alterations linked to reduced food quality. For instance, transfer of "high starch" and "crisp chip" traits from Solanum chacoense to cultivated potato (S. tuberosum) increased glycoalkaloid levels in the resulting variety "Lenape" to almost twice the maximum allowed concentration (354 mg kg-1; Zitnack and Johnson 1970).

One new extension of the plant breeding process specifically alters the expression of one or several of the plant's own genes without affecting the overall structure of the plant's genome. This new "intragenic" approach to genetic engineering employs marker-free systems to introduce all-native transfer DNAs into plants (Nielsen 2003; Rommens et al. 2004, 2007). For instance, it increases the expression of a key gene in a biosynthetic pathway by linking this gene to the strong promoter of a different native gene. Alternatively, a silencing construct is used to down-regulate the expression of a gene that is linked to an undesirable trait.

C.M. Rommens

Simplot Plant Sciences, J.R. Simplot Company, Boise, ID 83706, USA e-mail: [email protected]

F. Kempken and C. Jung (eds.), Genetic Modification of Plants, 61

Biotechnology in Agriculture and Forestry 64,

DOI 10.1007/978-3-642-02391-0_4, © Springer-Verlag Berlin Heidelberg 2010

In this review, we provide an update on efforts to develop and implement methods for the intragenic modification of important solanaceous and cruciferous crops as well as alfalfa (Medicago sativa), perennial ryegrass (Lolium perenne), and apple (Malus domestica). Most of the genetic elements and marker-free transformation methods employed are available to the scientific community for research purposes.

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