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MBE Advance Access originally published online on April 16, 2008
Molecular Biology and Evolution 2008 25(7):1482-1487; doi:10.1093/molbev/msn096
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Articles

Molecular Cloning and Characterization of a Moss (Ceratodon purpureus) Nonsymbiotic Hemoglobin Provides Insight into the Early Evolution of Plant Nonsymbiotic Hemoglobins

Verónica Garrocho-Villegas and Raúl Arredondo-Peter

Laboratorio de Biofísica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos, México

E-mail: ra{at}buzon.uaem.mx.

Accepted for publication April 7, 2008.

Nonsymbiotic hemoglobins (nsHbs) are widespread in plants including bryophytes. Bryophytes (such as mosses) are among the oldest land plants, thus an analysis of a bryophyte nsHb is of interest from an evolutionary perspective. However, very little is known about bryophyte nsHbs. Here, we report the cloning and characterization of an nshb gene (cerhb) from the moss Ceratodon purpureus. Sequence analysis showed that cerhb is interrupted by 3 introns in identical position as all known plant nshb genes, which suggests that the ancestral nshb gene was interrupted by 3 introns. Expression analysis showed that cerhb expresses in protonemas and gametophytes growing in normal conditions and that it overexpresses in protonemas subjected to osmotic (sucrose), heat-shock, cold-, and nitrate-stress conditions. Also, modeling of the Ceratodon nsHb (CerHb) tertiary structure suggests that CerHb is hexacoordinate and that it binds O2 with high affinity. Comparative analysis of the predicted CerHb with native rice Hb1 and soybean leghemoglobin a structures revealed that the major evolutionary changes that probably occurred during the evolution of plant Hbs were 1) a hexacoordinate to pentacoordinate transition at the heme prosthetic group, 2) a length decrease at the CD-loop and N- and C-termini regions, and 3) the compaction of the protein into a globular structure.

Key Words: Ceratodon • evolution • gene expression • globin • molecular modeling • nonsymbiotic

Geoffrey McFadden, Associate Editor


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