A zero-background CRISPR binary vector system for construction of sgRNA libraries in plant functional genomics applications

Mutation of GmIPK1 Gene Using CRISPR/Cas9 Reduced Phytic Acid Content in Soybean Seeds

Phytic acid (PA) acts as an antinutrient substance in cereal grains, disturbing the bioavailability of micronutrients, such as iron and zinc, in humans, causing malnutrition. GmIPK1 encodes the inositol 1,3,4,5,6-pentakisphosphate 2-kinase enzyme, which converts myo-inopsitol-1,3,4,5,6-pentakisphosphate (IP₅) to myo-inositol-1,2,3,4,5,6-hexakisphosphate (IP₆) in soybean (Glycine max L.). In this study, for developing soybean with low PA levels, we attempted to edit the GmIPK1 gene using the CRISPR/Cas9 system to introduce mutations into the GmIPK1 gene with guide RNAs in soybean (cv. Kwangankong). The GmIPK1 gene was disrupted using the CRISPR/Cas9 system, with sgRNA-1 and sgRNA-4 targeting the second and third exon, respectively. Several soybean Gmipk1 gene-edited lines were obtained in the T₀ generation at editing frequencies of 0.1–84.3%. Sequencing analysis revealed various indel patterns with the deletion of 1–9 nucleotides and insertions of 1 nucleotide in several soybean lines (T₀). Finally, we confirmed two sgRNA-4 Gmipk1 gene-edited homozygote soybean T₁ plants (line #21-2: 5 bp deletion; line #21-3: 1 bp insertion) by PPT leaf coating assay and PCR analysis. Analysis of soybean Gmipk1 gene-edited lines indicated a reduction in PA content in soybean T₂ seeds but did not show any defects in plant growth and seed development.

C-to-G Base Editing Enhances Oleic Acid Production by Generating Novel Alleles of FATTY ACID DESATURASE 2 in Plants

The demand for vegetable oil, which is mainly used for dietary purposes and cooking, is steadily increasing worldwide. It is often desirable to reduce unsaturation levels of fatty acids in order to increase storage stability and reduce trans-fat generation during cooking. Functional disruption of FATTY ACID DESATURASE 2 (FAD2) prevents the conversion of monounsaturated oleic acid to polyunsaturated linoleic acid, thereby enhancing the production of the desirable oleic acid. However, FAD2 null alleles, due to growth defects under stress conditions, are impractical for agronomical purposes. Here, we aimed to attenuate FAD2 activity in planta while avoiding adverse growth effects by introducing amino-acid substitutions using CRISPR base editors. In Arabidopsis, we applied the adenine base editor (ABE) and cytosine base editor (CBE) to induce semi-random base substitutions within several selected FAD2 coding regions. Isolation of base-edited fad2 alleles with higher oleic acid revealed that the CBE application induced C-to-T and/or C-to-G base substitutions within the targeted sequences, resulting in an alteration of the FAD2 enzyme activities; for example, fad2-144 with multiple C-to-G base substitutions showed less growth defects but with a significant increase in oleic acids by 3-fold higher than wild type. Our "proof-of-concept" approach suggests that equivalent alleles may be generated in vegetable oil crops via precision genome editing for practical cultivation. Our targeted semi-random strategy may serve as a new complementary platform for planta engineering of useful agronomic traits.