Advanced genetic tools for plant biotechnology

Key Points There are several emerging genetic tools that will have increasingly important roles in the future of plant biotechnology and crop genetics. Precise transgene or endogenous gene expression can be regulated at the transcriptional level by novel synthetic promoters, as well as synthetic transcriptional activators and repressors, for increased spatio-temporal control. The recent development of several advanced DNA construction and assembly methods will allow the production of long DNA constructs and vectors that are needed for multigene transformation into plants. Plant transformation with large constructs that are needed for metabolic pathway engineering is enabled by several techniques, including plant artificial chromosomes. There is no clear 'winner' among the several techniques presented. Plant-genome editing using a host of new tools, including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPRs), is poised to have, perhaps, the greatest effect on precisely changing DNA sequences in crops in novel ways. Tools for transgene removal and confinement are crucial for the commercialization of certain crops and crop–transgene combinations to ensure biosafety and government regulatory compliance. New tools for plant biotechnology are emerging, including synthetic promoters, 'tunable' transcription factors, genome-editing tools and site-specific recombinases. These tools promise to expand the range of plant biotechnology applications, especially when integrated with approaches for manipulating large DNA constructs. Basic research has provided a much better understanding of the genetic networks and regulatory hierarchies in plants. To meet the challenges of agriculture, we must be able to rapidly translate this knowledge into generating improved plants. Therefore, in this Review, we discuss advanced tools that are currently available for use in plant biotechnology to produce new products in plants and to generate plants with new functions. These tools include synthetic promoters, 'tunable' transcription factors, genome-editing tools and site-specific recombinases. We also review some tools with the potential to enable crop improvement, such as methods for the assembly and synthesis of large DNA molecules, plant transformation with linked multigenes and plant artificial chromosomes. These genetic technologies should be integrated to realize their po