Figueroa-Martinez F., Jackson C.J. & Reyes-Prieto A.
Plastid genomes from diverse glaucophyte genera reveal a largely conserved gene content and limited architectural diversity
Genome Biology and Evolution: in press


Plastid genome (ptDNA) data of Glaucophyta has been limited for many years to the genus Cyanophora. Here we sequenced the ptDNAs of Gloeochaete wittrockiana, Cyanoptyche gloeocystis, Glaucocystis incrassata and Glaucocystis sp. BBH. The reported sequences are the first genome-scale plastid data available for these three poorly studied glaucophyte genera. Although the Glaucophyta plastids appear morphologically "ancestral", they actually bear derived genomes not radically different from those of red algae or viridiplants. The glaucophyte plastid coding capacity is highly conserved (112 genes shared) and the architecture of the plastid chromosomes is relatively simple. Phylogenomic analyses recovered Glaucophyta as the earliest diverging Archaeplastida lineage, but the position of viridiplants as the first branching group was not rejected by the approximately unbiased test. Pairwise distances estimated from 19 different plastid genes revealed that the highest sequence divergence between glaucophyte genera is frequently higher than distances between species of different classes within red algae or viridiplants. Gene synteny and sequence similarity in the ptDNAs of the two Glaucocystis species analyzed is conserved. However, the ptDNA of Glaucocystis incrassata contains a 7.9kb insertion not detected in Glaucocystis sp. BBH. The insertion contains 10 ORFs that include four coding regions similar to bacterial serine recombinases (two ORFs), DNA primases and peptidoglycan aminohydrolases. These three enzymes, often encoded in bacterial plasmids and bacteriophage genomes, are known to participate in the mobilization and replication of DNA mobile elements. It is therefore plausible that the insertion in Glaucocystis incrassata ptDNA is derived from a DNA mobile element.

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