Chloroplast Genomics for Sustainable Cotton Production

Plants are unique in that their cells contain three genomes: in the nucleus, mitochondria, and chloroplasts. Advances in recombinant DNA technology allow the manipulation of all three genomes. Insertion of foreign genes in the nucleus results in low gene expression, random integration of the transgenes, and gene silencing due to epigenetic interactions. Introducing transgenes into the chloroplast genome offers several advantages that include extraordinary gene expression levels (>70% of total soluble proteins), uniform gene expression due to non-Mendelian inheritance, and site-specific integration of the transgene at a chosen location on the chloroplast genome. The most attractive feature of developing transgenic field crops perhaps lies in the fact that chloroplast DNA is not carried in the pollen, particularly in field crops. The inheritance of chloroplasts in angiosperms is predominantly maternal, thereby providing a natural transgene containment system. Despite the huge potential, chloroplast transformation has not been extended to field crops, particularly cotton. There is only one study reporting the development of transgenic cotton expressing a kanamycin selectable marker. The possible reasons that currently hinder the application of this technology to cotton include prolonged and inefficient tissue culture-based protocols for recovering transplastomic plants and the limitation to develop transgenic plants from nongreen plastids through somatic embryogenesis. Efforts are underway to extend chloroplast transformation in agronomically important crops. In this chapter, we highlight the potential of chloroplast transformation technology for developing transgenic cotton for sustainable cotton production.