Use of cyanobacterial proteins to engineer new crops

Abstract

Cyanobacteria, the closest living relatives of the ancient endosymbiont that gave rise to modern-day chloroplasts, offer a rich source of genes for plant genetic engineering, due to both similarities with and differences from the plant genetic systems. On the one hand, cyanobacteria share many metabolic pathways with plant cells, and especially with chloroplasts, which may be critical when the transgenic product needs to interact with endogenous systems or substrates to exert its function. On the other hand, most mechanisms involved in plant regulation of gene expression have arisen after endosymbiosis, permitting a more rational manipulation of the introduced trait, free from host regulatory networks. In addition, sequence divergence between plant genes and their cyanobacterial orthologues prevents, in most cases, the unwanted consequences of gene silencing and cosuppression. Finally, a few cyanobacterial genes involved in tolerance to environmental and/or nutritional stresses have disappeared from the plant genome during the evolutionary pathway from cyanobacteria to vascular plants, raising the possibility of recovering these adaptive advantages by introducing those lost genes into transgenic plants. In spite of their obvious potential, the use of cyanobacterial genes to engineer plants for increased productivity or stress tolerance has been relatively rare. In this chapter, we review several examples in which this approach has been applied to plant genetic engineering with considerable success. They include modification of central metabolic pathways to improve carbon assimilation and allocation by expressing unregulated cyanobacterial enzymes, development of chilling tolerance by increasing desaturation of membrane-bound fatty acids, pigment manipulation, shifts in light quality perception, production of biodegradable polymers, and synthesis of ketocarotenoids not present in crops. Tolerance to adverse environments could be achieved by the introduction of cyanobacterial genes lost from the plant genome during evolution, such as flavodoxin. The results obtained illustrate the power of gene and data mining in cyanobacterial genomes as a biotechnological tool for the design of transgenic plants with higher productivity, enhanced tolerance to environmental stress, and potential for biofarming. © 2009 Springer-Verlag US.