Deciphering pathways of chloroplast and mitochondrial genome evolution in green algae

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All eukaryotic cells feature membrane-bound organelles containing DNA, called mitochondria and (in algae and land plants) chloroplasts. By studying the genes encoded in these vital cellular components involved in energy production, researchers have found that in several eukaryotic lineages, including green algae and land plants, the chloroplast (cp) and mitochondrial (mt) genomes exhibit considerable diversity in size, structure, gene content, gene order and intron content. Our group is determining and analyzing the complete sequences of organelle genomes from green algae, which range in size from 20,000 to 350,000 bases. All living green plants (Viridiplantae) are divided into two phyla: the Chlorophyta, comprising the bulk of the green algae, and the Streptophyta, comprising the green algae from the class Charophyceae and all land plants. We have recently shown that the cp genome is evolving much more conservatively in the Streptophyta than in the Chlorophyta and that the cp genome of land plants inherited a myriad of traits from their charophycean green algal ancestors. In contrast, the mt genome sustained radical changes during the evolution of both chlorophytes and streptophytes and it appears that land plant mtDNAs inherited only a few structural characters from charophycean green algae. The aims of the proposed research are two-fold: (1) to understand how streptophyte and chlorophyte organelle genomes diverged over evolutionary time and (2) to resolve the branching order of problematic green algal lineages in the tree of life. Complete cpDNA and mtDNA sequences from representatives of various green algal lineages will be determined, decoded, and compared to their previously sequenced green plant homologs. Using a phylogenic framework inferred from whole organelle genomes, we will be reconstruct scenarios of gene losses, gene rearrangements and intron gains/losses. The information gained will help us to decipher the forces that shape organelle genomes. This information is also crucial for understanding how green algae evolved and gave rise to land plants. We expect that the proposed studies will represent a major Canadian contribution in the area of organelle genomics.