Won Nyeong Kim, Hyun Uk Kim
SUMMARY Diacylglycerol acyltransferase 1 (DGAT1) catalyzes the final step in triacylglycerol (TAG) biosynthesis and is a key determinant of seed oil content and composition. To dissect the functional contribution of the conserved DGAT1 domains, we employed adenine and cytosine base editors and CRISPR/Cas9-mediated in-frame deletion to generate targeted alleles in Arabidopsis thaliana . A total of 25 single guide RNAs were designed to introduce precise nucleotide substitutions across functional domains, and the edited lines were screened using seed fluorescence and Sanger sequencing. Five base-edited (BE) DGAT1 mutants affecting acyl-CoA/CoA allosteric binding site (S124F, S123R/S124L), thiolase acyl-enzyme intermediate signature motif (L229P), diacylglycerol (DAG)-binding motif (W416C/R419Q, V418I), and an in-frame deletion in the intrinsically disordered N-terminal region (Δ49-76::H) were characterized. Amino acid substitutions in the conserved domains led to distinct shifts in seed fatty acid profiles. Loss-of-function-like mutants (S123R/S124L, L229P, W416C/R419Q) reduced 18:1 and 20:1 levels and increased 18:3 levels, whereas putative gain-of-function mutants (S124F, V418I) enhanced 20:1 incorporation and elevated total oil content. Overexpression of DGAT1 S124F and DGAT1 V418I in the dgat1 mutant background further increased seed oil accumulation beyond that achieved with wild-type DGAT1. Structural modeling of DGAT1 proteins revealed the location of substituted amino acids and their interactions with surrounding residues, as well as the absence of putative N-terminal regulatory segment. These results demonstrate that precise base editing can modulate DGAT1 activity and TAG composition by targeting functional motifs, providing insights into the structure–function relationships of this key enzyme and offering strategies for metabolic engineering of seed oils.