Challenges and emerging solutions
Agriculture is faced with an urgent need to evolve in response to the global challenges of the 21 century. The recently released IPCC climate report indicates a faster progression of climate change than previously expected. Climate models predict severe impacts for agriculture on a global level. In Europe, severe impact on yield due to temperature increase and changes in precipitation is imminent [1]. Globally major impacts of soil erosion in tropical regions will reduce the farmable area [2]. Currently classical breeding for spring wheat can barely mitigate the existing yield affecting factors, and the situation is projected to get worse [1]. Looking into other aspects agriculture needs to battle, like the impact of pests, biodiversity, soil depletion and extensive fertilizer and chemical use, it is evident that a second green revolution of agriculture and plant breeding is urgently needed.
The advent of site-specific nuclease (SSN) based genome editing technologies have resulted in a great interest in their applications in plant breeding. Much emphasis has been placed on the ability of genome editing technologies to introduce beneficial mutations in an elite genetic background without the high number of background mutations or linkage drag associated with conventional approaches. However, this ‘precision breeding’ strategy has limitations 1) it requires knowledge about the identity and function of the target gene and 2) it only applies to traits which can be modified through one or a few genes. A different strategy is clearly in need for exploiting the full diversity of adaption found in nature. We propose that the answer may lie in turning the concept of precision breeding upside down. Rather than attempting to first understand and then re-engineer the complex genetic networks that confer environmental adaptation to wild plants, it may be more feasible to acquire these networks for agriculture by domesticating the wild plant itself.
The major stable crops of the modern world were domesticated in prehistoric times and perfected over millennia. Although there are some examples of modern domestication like blueberries, blackberries or strawberries, these novelty crops do not compete directly with the staples [3-5]. It is undoubtedly a bold proposal to re- or de novo - domesticate staple crops. However, we do so because we see the synergy of progress in two areas. Genome editing technology and molecular characterization of the genes behind the domestication syndrome in major crops. Thus, it should be feasible to accomplish or repeat domestication by the application of genome editing to wild plants by using already domesticated relatives as a roadmap. We propose to call that approach “G enome E diting a cceleratedRe -D omestication” (GEaReD ) (see Fig. 1).
GEaReD rely on the natural selection happened over millions of years to secure adaptation and resilience. Agronomic and possibly food safety traits are then introduced with techniques such as CRISPR/Cas9, CRISPR/Cas9 Integrase/Isomerase or PRIME-CRISPR to create highly adapted plants with yield and quality that can compete with current cultivars (see Fig. 1). Since Genome Editing can accelerate breeding substantially, it would be possible to generate new cultivars in 2-4 years compared to the current much longer timeframe. The road tode novo domestication of wild plants for new breeding material or even new cultivars has never been shorter. The first examples include the de novo domestication of a ground cherry (Physalis pruinosa ) and wild tomatoes [6, 7]. These first reports were shortly followed by reports on cereal de novo domestication. Recently work on African rice landraces, and their ability to accelerate domestication and development by CRISPR-mediated genome editing was published [8]. Furthermore, a roadmap including the necessary tools and examples of their application for the domestication of allotetraploid rice has been provided [9].