Automated linear DNA assembly of <i>A. thaliana’</i> 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.