ABSTRACT
The root system serves many tasks; it anchors the plant and absorbs water and minerals from the soil and delivers certain growth regulators. Roots also have the remarkable ability to secrete a vast array of low-and high-molecular-weight molecules into the rhizosphere in response to bio tic and abiotic stresses. The underground growth habit and the lack of suitable experimental systems to approach roots directly made root research problematic in the past. In the past 10 years, progress in root biology has been made by using molecular-genetic tools, thus offering novel perspectives for both the understanding and exploitation of root processes. In molecular root bioengineering genetic engineering principles are applied to problems involving root cells, tissues, or molecules that exert biological activity at the level of the plant root. A prerequisite for successful application of molecular-genetic tools toward modification of root functions is the characterization of tissue-specific gene expression, the isolation of suitable promoters, and the characterization of gene function. The expression of endogenous or heterologous genes can then be directed in a precise spatial and temporal manner to modify and improve root properties. This chapter attempts to give insight into molecular approaches in root research and to point out opportunities for root bioengineering. It includes an overall view of standard and modern methods suitable to investigate root-specific gene expression. Examples for the control of root gene expression by environmental factors such as nutrient availability, interacting symbiontic organisms, or pathogens will be given. Finally, recently published promising applications in molecular root bioengineering will be presented.
