A comparative analysis of plant mitochondrial small subunit ribosomal RNA sequences.

The small subunit of the ribosomal RNA has long been used as a tool in determining phylogenetic relationships. This project explored a region of the mitochondrial small subunit ribosomal RNA (MSrRNA) that is found only in the plant mitochondrial genome referred to as Variable Region 7 (V7). The V7 region of cauliflower and radish, both members of the Brassicaceae family, was amplified with the polymerase chain reaction, cloned into the expression vector PBSSK +, and sequenced. There was only a 0.3% sequences difference between the cauliflower and radish V7 region, thus suggesting that there will not be sequence variation in this region within a plant species. Cauliflower and radish V7 sequence was compared with the 6 other sequences of plant MSrRNA V7 region available: wheat, corn, oats, evening primrose, soybean and lupine. Based on percent difference between the V7 region sequences, a phylogenetic tree was constructed that supports the placement of these 8 species in Cronquist's morphologically based phylogenetic tree of flowering plants.