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Occurrence of matK in a trnK group II intron in charophyte green algae and phylogeny of the Characeae¹

²Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1737 USA; ³Cell Biology and Molecular Genetics/Plant Biology, 2106 H. J. Patterson Hall, Building 073, University of Maryland, College Park, Maryland 20742-5815 USA; ⁴Department of Botany, Academy of Natural Sciences, 1900 Benjamin Franklin Parkway, Philadelphia, Pennsylvania 19103 USA

A group II intron containing the matK gene, which encodes a splicing-associated maturase, was found in the trnK (lysine tRNA) exon in the chloroplast genome of the six extant genera of green algae in the family Characeae, which among green algae are the sister group to embryophytes (land plants). The characean trnK intron (2.5 kilobases [kb]) and matK ORF (1.5 kb) are comparable in size to the intron and ORF of land plants, in which they are similarly found inserted in the trnK exon. Domain X, a sequence of conserved amino acid residues within matK, occurs in the Characeae. Phylogenetic analysis using maximum likelihood (GTR + I + gamma likelihood model) and parsimony (branch and bound search) yielded one tree with high bootstrap support for all branches. The matK tree was congruent with the rbcL tree for the same taxa. The number and proportion of informative sites was higher in matK (501, 31% of matK sequence) compared to rbcL (122, 10%). Characeae branch lengths were on average more than five times longer for matK compared to rbcL and provided better resolution within the Characeae. These findings along with recent genomic analyses demonstrate that the intron and matK invaded the chloroplast genome of green algae prior to the evolution of land plants.

Key Words: Characeae • charophyte green algae • matK • maturase • rbcL • trnK

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				G. Hausner, R. Olson, D. Simon, I. Johnson, E. R. Sanders, K. G. Karol, R. M. McCourt, and S. Zimmerly Origin and Evolution of the Chloroplast trnK (matK) Intron: A Model for Evolution of Group II Intron RNA Structures Mol. Biol. Evol., February 1, 2006; 23(2): 380 - 391. [Abstract] [Full Text] [PDF]