Plant Plastid Engineering

Wani, Shabir H.; Haider, Nadia; Kumar, Hitesh; Singh, N.B.

Genetic material in plants is distributed into nucleus and the chloroplast and mitochondria in the cytoplasm. Each of these three compartments carries its own genome and expresses heritable traits [1, 2] . The chloroplast is one of organelles known as plastids in plant cells and eukaryotic algae [3] . According to Verhounig et al. [4] , plastids and mitochondria are derived from formerly free-living bacteria and have largely prokaryotic gene expression machinery. The plastid (biosynthetic centre of the plant cell) carries out photosynthesis, in plant cells and eukaryotic algae, which provides the primary source of the world's food [3] . There are other important activities that occur in plastids. These include sequestration of carbon, production of starch, evolution of oxygen, synthesis of amino acids, fatty acids, and pigments, and key aspects of sulfur and nitrogen metabolism [5] . In spite of the prokaryotic past of the plastids, their gene expression has very different regulatory mechanisms from those operating in bacteria [6] . There are up to 300 plastids [7] in one plant cell. The plastid genome (plastome or plastid DNA, ptDNA), 1,000-10,000 copies per cell [8] , contrasts strikingly with the nuclear DNA. In most species, plastids are usually strictly maternally inherited [9] in most (80%) angiosperm plant species [10, 11] . It is also not influenced by polyploidy, gene duplication and recombination that are widespread features of the nuclear genomes of plants [12, 13] . Therefore, ptDNA varies little among angiosperms in terms of size, structure and gene content [14] . Currently 170 DNA. The authors, therefore, developed a simple and inexpensive method to obtain plastid DNA from grass species by modifying and extending protocols optimized for the use in eudicots. Plastid engineering involves the targeting of foreign genes to the plastid's double-stranded circular DNA genome instead of chromosomal DNA [31] , and as a consequence the production of the foreign protein of interest (Fig. 1) . The advancement in the particle gun mediated transformation has enabled targeting the plastid genome for developing transgenic plants against many biotic (e.g. insects and pathogens) and abiotic stresses (e.g. drought and salinity), which reduce the plant productivity. Improving the quality of fruits has been another main target in plastid transformation [32] .