Sequence of the plastid rDNA spacer region of the brown alga Pylaiella littoralis (L.) Kjellm. Evolutionary significance

The DNA segment situated between the 16S and 23S rRNA genes belonging to the plastid genome of the brown alga Pylaiella littoralis (L.) Kjellm. has been sequenced. This small region (322 bp) contains two unsplit tRNA genes separated by 3 bp. A comparison with similar regions from different plants shows that this region has evolved in two different ways according to the place of plants in evolution. In the primitive group, this region is reduced in size when compared to prokaryotes. In the other groups, it is considerably enlarged by insertion of repetitive sequences, open reading frames and introns.