The Escherichia coli RNA polymerase (RNAP) α, β, and β' core subunits are evolutionarily conserved among bacteria and plastids, and the plastid specificity factors form a functional holoenzyme with the E. coli core. To investigate whether the E. coli core subunits may form a functional hybrid enzyme with the plastid core subunits, we replaced the tobacco plastid RNAP α subunit gene (rpoA) with the E. coli α subunit gene by targeted gene insertion. The transplastomic tobacco plants look similar to tobacco rpoA deletion mutants in that they are chlorophyll-deficient and non-photoautotrophic. In addition, they lack transcripts from promoters recognized by the E. coli-like plastid RNA polymerase. These results indicate that evolutionary conservation between the E. coli and plastid RNA polymerase α subunits is insufficient to allow substitution of the tobacco α subunit with its bacterial counterpart. Interestingly, the cyanobacterial α subunits are as different as the E. coli α subunits; and therefore it is unlikely that replacement of the tobacco α subunit with cyanobacterial α subunits would yield a functional enzyme. Replacement of plastid rpoA with the E. coli RNA polymerase α subunit gene represents the first engineering of a plastid operon in higher plants.
All Science Journal Classification (ASJC) codes
- Escherichia coli RNA polymerase α subunit
- Plastid RNA polymerase
- Plastid transcription
- Transplastomic tobacco