Enhancing plant fatty acid synthesis through plastid accd promoter engineering

Overview

This research proposes a targeted gene-editing strategy to increase fatty acid (FA) production in oilseed crops such as rapeseed and soybean. The approach focuses on the plastid-encoded accD gene, which encodes the beta subunit of acetyl-CoA carboxylase (ACCase), the enzyme that catalyzes the first committed step in fatty acid biosynthesis. Because accD transcription is naturally limited by the fact that its promoter is recognized only by the nuclear-encoded plastid RNA polymerase (NEP), the team hypothesizes that adding cis-elements recognized by the plastid-encoded polymerase (PEP) will increase accD expression, ACCase abundance, and ultimately fatty acid levels. The work has potential applications in crop improvement, oilseed yield enhancement, and sustainable agricultural biotechnology.

Technical specifications

• Target gene: Plastid-encoded accD, the beta subunit of acetyl-CoA carboxylase, the rate-limiting enzyme in fatty acid biosynthesis
• Editing tool: Transcription-activator-like-effector directed Cytosine Deaminase (TALE-CD), which enables precise C-to-T base editing without cutting the DNA
• Editing strategy: Modification of the accD promoter by converting a candidate sequence (CACAAT) near the transcription start site into a PEP-type -10 motif (TATAAT), creating a hybrid promoter recognized by both NEP and PEP
• Validation precedent: In tobacco, replacing the accD promoter with a NEP+PEP-type plastid rRNA promoter via plastid transformation increased accD and ACCase expression, doubling seed yield and fatty acid production
• Editing efficiency: TALE-CD has demonstrated greater than 90 percent editing efficiency in Arabidopsis plastids for C-to-T conversions in psbA coding sequences
• Host system: Initial validation is planned in Arabidopsis, with downstream applicability to oilseed crops

Technology readiness level

The technology is currently at an early-to-mid stage of development. Proof-of-concept evidence exists from tobacco studies showing that promoter engineering of accD can double seed yield and fatty acid production. Preliminary bioinformatic analysis in Arabidopsis has identified a candidate promoter sequence amenable to TALE-CD editing, and the editing tool itself has been validated for high-efficiency plastid base editing. The proposed next steps include vector construction, generation of edited Arabidopsis lines, characterization of fatty acid composition and abundance, seed yield analysis, and off-target sequencing of the chloroplast genome. Successful completion of these steps would establish readiness for translation into oilseed crops such as rapeseed and soybean.