Positive-selection and ligation-independent cloning vectors for large scale in planta expression for plant functional genomics.

Abstract

Transient expression is an easy, rapid and powerful technique for producing proteins of interest in plants. Recombinational cloning is highly efficient but has disadvantages, including complicated, time consuming cloning procedures and expensive enzymes for large-scale gene cloning. To overcome these limitations, we developed new ligation-independent cloning (LIC) vectors derived from binary vectors including tobacco mosaic virus (pJL-TRBO), potato virus X (pGR106) and the pBI121 vector-based pMBP1. LIC vectors were modified to enable directional cloning of PCR products without restriction enzyme digestion or ligation reactions. In addition, the ccdB gene, which encodes a potent cell-killing protein, was introduced between the two LIC adapter sites in the pJL-LIC, pGR-LIC, and pMBP-LIC vectors for the efficient selection of recombinant clones. This new vector does not require restriction enzymes, alkaline phosphatase, or DNA ligase for cloning. To clone, the three LIC vectors are digested with SnaBI and treated with T4 DNA polymerase, which includes 3' to 5' exonuclease activity in the presence of only one dNTP (dGTP for the inserts and dCTP for the vector). To make recombinants, the vector plasmid and the insert PCR fragment were annealed at room temperature for 20 min prior to transformation into the host. Bacterial transformation was accomplished with 100% efficiency. To validate the new LIC vector systems, we were used to coexpressed the Phytophthora AVR and potato resistance (R) genes in N. benthamiana by infiltration of Agrobacterium. Coexpressed AVR and R genes in N. benthamiana induced the typical hypersensitive cell death resulting from in vivo interaction of the two proteins. These LIC vectors could be efficiently used for high-throughput cloning and laboratory-scale in planta expression. These vectors could provide a powerful tool for high-throughput transient expression assays for functional genomic studies in plants.