Ribosomal RNA Genes and Pseudogenes of the Bi-Molecular Plastid Genome of the Brown Alga Pylaiella littoralis

Abstract

The algae have long been classified into three main groups based on their plastidial pigments (Christensen, 1964). In this scheme all three groups have the same primary pigment, chlorophyll a, and the different taxa are defined by their secondary pigments; the green algae having chlorophyll b, the red algae having phycobilins, and the chromophytes (which include the brown algae), having chlorophyll c. Today, plastidial characters are still viewed as important in defining the relationships among the algae, and between the algae and higher plants. In this light, some of the most intriguing questions about the chromophytes concern the different morphologies, origins, and evolutionary histories of their plastids. One way to study these organelles is to examine them at the genomic level and to compare both the gross organization and fine structure of their genes with those of other plastids (not only green plastids) and prokaryotes (not only cyanobacteria). For this purpose, we have begun an extensive investigation of the plastidial genome of a simple brown alga, Pylaiella littoralis (L.) Kjellm. Herein we describe progress to date in characterizing the ribosomal operons, genes and pseudogenes found on this genome, and we discuss the phylogenetic implications of these results.