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Genes of Cyanobacterial Origin in Plant Nuclear Genomes Point to a Heterocyst-Forming Plastid Ancestor
 

Summary: Genes of Cyanobacterial Origin in Plant Nuclear Genomes Point to
a Heterocyst-Forming Plastid Ancestor
Oliver Deusch,* Giddy Landan, Mayo Roettger,* Nicole Gruenheit,* Klaus V. Kowallik,*
John F. Allen,à William Martin,* and Tal Dagan*
*Institut fu¨r Botanik III, Heinrich-Heine Universita¨t Du¨sseldorf, Universita¨tsstrasse 1, Du¨sseldorf, Germany; Department of Biology
and Biochemistry, University of Houston; and àSchool of Biological and Chemical Sciences, Queen Mary, University of London,
London, United Kingdom
Plastids are descended from a cyanobacterial symbiosis which occurred over 1.2 billion years ago. During the course of
endosymbiosis, most genes were lost from the cyanobacterium's genome and many were relocated to the host nucleus
through endosymbiotic gene transfer (EGT). The issue of how many genes were acquired through EGT in different plant
lineages is unresolved. Here, we report the genome-wide frequency of gene acquisitions from cyanobacteria in 4
photosynthetic eukaryotes--Arabidopsis, rice, Chlamydomonas, and the red alga Cyanidioschyzon--by comparision of
the 83,138 proteins encoded in their genomes with 851,607 proteins encoded in 9 sequenced cyanobacterial genomes,
215 other reference prokaryotic genomes, and 13 reference eukaryotic genomes. The analyses entail 11,569 phylogenies
inferred with both maximum likelihood and Neighbor-Joining approaches. Because each phylogenetic result is
dependent not only upon the reconstruction method but also upon the site patterns in the underlying alignment, we
investigated how the reliability of site pattern generation via alignment affects our results: if the site patterns in an
alignment differ depending upon the order in which amino acids are introduced into multiple sequence alignment--N- to
C-terminal versus C- to N-terminal--then the phylogenetic result is likely to be artifactual. Excluding unreliable
alignments by this means, we obtain a conservative estimate, wherein about 14% of the proteins examined in each plant

  

Source: Allen, John F. - School of Biological and Chemical Sciences, Queen Mary, University of London

 

Collections: Renewable Energy; Biology and Medicine