Automated linear DNA assembly of A. thaliana's chloroplast and mitochondrial genome

Synthetic genomics is advancing from microbial toward multicellular organisms. However, current manual methods for DNA and genome assembly remain inadequate for the efficient, large-scale production of long DNA constructs. Here, we present Programmed DNA Assembly via Cas9 and Conjugative Transfer (PACT), a method that integrates a linear vector system, bacterial conjugation, and programmable Cas9-mediated cleavage to achieve highly efficient, iterative assembly of large DNA fragments. PACT enhances assembly efficiency by ~30-fold compared to conventional circular vector strategies, enabling one-step assembly of DNA up to 80 kb. We engineered four single guide-RNA-Marker donor cassettes to support iterative assembly workflows. PACT can utilize low-recombination Escherichia coli strains as hosts to efficiently assemble Arabidopsis thaliana mitochondrial genome with high repeat units. Integrated with an automated robotic platform, we developed an unattended, high-throughput pipeline (aPACT) toward large-scale parallel DNA assembly. Using aPACT, we successfully assembled three large DNA constructs: a 210 kb digital DNA, the designed chloroplast (120 kb) and mitochondrial (350 kb) genome of A. thaliana. This automated system offers a powerful tool for scalable assembly of large DNA molecules, accelerating synthetic genomics research toward complex multicellular organisms.