The Genetic Engineering Toolbox for Transformation of Higher Plant Plastids

Plastids are membrane-bound organelles that assume a wide range of essential functions in the plant kingdom, ranging from photosynthesis to coordinating with other compartments in important biosynthesis of metabolites. During the evolution of plant cells, this class of organelles originated from an event of endosymbiosis between a cyanobacterium and an early eukaryotic cell. After this first incorporation, this prokaryotic progenitor progressively lost the peculiar characteristic of an autonomous genetic system, evolving into an organelle with essential functions in what we know today as plant cells. However, modern plastids still preserve several prokaryotic-like features, including the retention of a genome (the plastome), and other aspects related to the transcription and translation machineries that enable plastids to express genes arranged in operons. These characteristics, along with the central role of plastids in many endogenous metabolic pathways, make this group of organelles valuable targets for plant genetic engineering applications. In this chapter we describe the fundamental aspects of plastid genetic engineering, from the design of transformation vectors for delivery of transgenes, to methods for production of stable transgenic (transplastomic) plants in tissue culture. This chapter will also provide a description of the current progress in designing novel genetic tools and future challenges in plastid genetic engineering.