Crop genome editing: A way to breeding by design

Creating a zero amylose barley with high soluble sugar content by genome editing

Amylose biosynthesis is strictly associated with granule-bound starch synthase I (GBSSI) encoded by the Waxy gene. Mutagenesis of single bases in the Waxy gene, which induced by CRISPR/Cas9 genome editing, caused absence of intact GBSSI protein in grain of the edited line. The amylose and amylopectin contents of waxy mutants were zero and 31.73%, while those in the wild type were 33.50% and 39.00%, respectively. The absence of GBSSI protein led to increase in soluble sugar content to 37.30% compared with only 10.0% in the wild type. Sucrose and β-glucan, were 39.16% and 35.40% higher in waxy mutants than in the wild type, respectively. Transcriptome analysis identified differences between the wild type and waxy mutants that could partly explain the reduction in amylose and amylopectin contents and the increase in soluble sugar, sucrose and β-glucan contents. This waxy flour, which showed lower final viscosity and setback, and higher breakdown, could provide more option for food processing.

Establishment of an efficient seed fluorescence reporter-assisted CRISPR/Cas9 gene editing in maize

Genome editing by clustered regularly interspaced short palindromic sequences (CRISPR)/CRISPR-associated protein 9 (Cas9) has revolutionized functional gene analysis and genetic improvement. While reporter-assisted CRISPR/Cas systems can greatly facilitate the selection of genome-edited plants produced via stable transformation, this approach has not been well established in seed crops. Here, we established the seed fluorescence reporter (SFR)-assisted CRISPR/Cas9 systems in maize (Zea mays L.), using the red fluorescent DsRED protein expressed in the endosperm (En-SFR/Cas9), embryos (Em-SFR/Cas9), or both tissues (Em/En-SFR/Cas9). All three SFRs showed distinct fluorescent patterns in the seed endosperm and embryo that allowed the selection of seeds carrying the transgene of having segregated the transgene out. We describe several case studies of the implementation of En-SFR/Cas9, Em-SFR/Cas9, and Em/En- SFR/Cas9 to identify plants not harboring the genome-editing cassette but carrying the desired mutations at target genes in single genes or in small-scale mutant libraries, and report on the successful generation of single-target mutants and/or mutant libraries with En-SFR/Cas9, Em-SFR/Cas9, and Em/En-SFR/Cas9. SFR-assisted genome editing may have particular value for application scenarios with a low transformation frequency and may be extended to other important monocot seed crops.

Herbicide Resistance: Another Hot Agronomic Trait for Plant Genome Editing

Weeds have continually interrupted crop plants since their domestication, leading to a greater yield loss compared to diseases and pests that necessitated the practice of weed control measures. The control of weeds is crucial to ensuring the availability of sufficient food for a rapidly increasing human population. Chemical weed control (herbicides) along with integrated weed management (IWM) practices can be the most effective and reliable method of weed management programs. The application of herbicides for weed control practices calls for the urgency to develop herbicide-resistant (HR) crops. Recently, genome editing tools, especially CRISPR-Cas9, have brought innovation in genome editing technology that opens up new possibilities to provide sustainable farming in modern agricultural industry. To date, several non-genetically modified (GM) HR crops have been developed through genome editing that can present a leading role to combat weed problems along with increasing crop productivity to meet increasing food demand around the world. Here, we present the chemical method of weed control, approaches for herbicide resistance development, and possible advantages and limitations of genome editing in herbicide resistance. We also discuss how genome editing would be effective in combating intensive weed problems and what would be the impact of genome-edited HR crops in agriculture.