Four Embryophyte Introns and psbB Operon Indicate Chlorokybus as a Basal Streptophyte Lineage

In the evolutionary history of life on Earth one of the most important events would arguably have to be the transition of aquatic algae into land plants (embryophytes). The goal of this study was to help paint a better picture of the evolution of algae to land plants. The gene cluster that includes psbB, psbT, psbH, petB and petD from the chloroplastic genome was examined in the five major lineages of charophytes.

It was found that the psbB gene cluster found in almost all charophytes and embryophytes except Spirogyra (Zygnematales) which lacks it due to intra-genomic rearrangement. All four introns are absent in Chlorokybus but present in some or all of the other four charophyte lineages (Klebsormidiales, Zygnematales, Coleochaetales, and Charales). Chlorokybus also has an unusually long spacer between psbH-petB, over 2 kb long. This result seems to show that Chlorokybus branched off before most of the introns were gained in the most of the charophytes but after the  psbB gene cluster was gained. PCR was used to clone the intron containing portion from total cellular DNA. But in a few of the species chloroplastic genomic DNA was used.

Jungho Lee and James R. Manhart. 2002. Four Embryophyte Introns and psbB Operon Indicate Chlorokybus as a Basal Streptophyte Lineage. Algae Vol. 17 (1): 53-58