Genome Editing for Crop Improvement – Applications in Clonally Propagated Polyploids With a Focus on Potato (Solanum tuberosum L.)

Abstract

Genome-editing has revolutionized biology. When coupled with a recently streamlined regulatory process by the U.S. Department of Agriculture and the potential to generate transgene-free varieties, genome-editing provides a new avenue for crop improvement. For heterozygous, polyploid and vegetatively propagated crops such as cultivated potato, Solanum tuberosum Group Tuberosum L., genome-editing presents tremendous opportunities for trait improvement. In potato, traits such as improved resistance to cold-induced sweetening, processing efficiency, herbicide tolerance, modified starch quality and self-incompatibility have been targeted utilizing CRISPR/Cas9 and TALEN reagents in diploid and tetraploid clones. However, limited progress has been made in other such crops including sweetpotato, strawberry, grapes, citrus, banana etc., In this review we summarize the developments in genome-editing platforms, delivery mechanisms applicable to plants and then discuss the recent developments in regulation of genome-edited crops in the United States and The European Union. Next, we provide insight into the challenges of genome-editing in clonally propagated polyploid crops, their current status for trait improvement with future prospects focused on potato, a global food security crop.

Reduced Enzymatic Browning in Potato Tubers by Specific Editing of a Polyphenol Oxidase Gene via Ribonucleoprotein Complexes Delivery of the CRISPR/Cas9 System

“…Foreign DNA integration into the plant genome is a major concern in genome editing techniques, and is preferably avoided when applied for commercial breeding purposes (Eckerstorfer et al, 2019). This is of special importance in a tetraploid and highly heterozygous crop like potato, since backcrossing techniques to eliminate inserted foreign DNA would lead to the loss of allelic combination in an elite variety (Nadakuduti et al, 2018). In some of the mutated lines identified in our study, insertions were observed in the target region, which corresponded to fragments of the DNA template used in the in vitro transcription of the sgRNAs, or potato genomic fragments.…”

“…The presence of multiple mismatches into the seed region (defined as the 8-12 nt proximal to the PAM) between the selected sgRNAs and the rest of StPPO genes could explain their specificity for StPPO2 (Hahn and Nekrasov, 2019). On the other hand, the use of RNPs as delivery method for the CRISPR/Cas9 system has been proposed to reduce the incidence of off targets effects, due to the rapid degradation of the Cas9 nuclease and the sgRNAs in the cell (Nadakuduti et al, 2018;Zhang et al, 2018a;Hahn and Nekrasov, 2019).…”

Applying the Solanaceae Strategies to Strawberry Crop Improvement

“…Once identified, their effect on the trait of interest can be validated in diploid or cultivated strawberry through, for example, virus-induced gene silencing [64] or stable transformation [15,16]. Gene editing technologies using transcription activator-like effector nucleases (TALENs) or the CRISPR/ Cas9 system are particularly attractive for engineering crops with desirable traits, as shown in many crop species including tomato, potato, and strawberry [65,66]. The CRISPR/Cas9 system has been successfully established in both Fragaria species [15,16].…”

Strategies to produce T-DNA free CRISPRed fruit trees via Agrobacterium tumefaciens stable gene transfer

“…Over the last few years, the development of genome editing techniques boosted green biotechnology research committed to crop improvement. Editing technology, based predominantly on CRISPR systems, has been applied to various crop species offering tremendous opportunities for trait improvement in vegetatively propagated crops, which can thus conserve the overall genetic make-up 1 , 2 . However, this huge biotechnological potential is sometimes hampered by legislative boundaries which regulate agricultural production at a national level.…”