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MBE Advance Access published online on April 16, 2008
Molecular Biology and Evolution, 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

Molecular Cloning and Characterization of a Moss (Ceratodon purpureus) Non-Symbiotic Hemoglobin Provides Insight into the Early Evolution of Plant Non-Symbiotic 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

* Corresponding author: Lab. de Biofísica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62210 Cuernavaca, Morelos, México; tel. no. +52(777)329-7020; fax no. +52(777)329-7040; E-mail ra{at}buzon.uaem.mx.

Received for publication March 11, 2008. Revision received March 31, 2008. Accepted for publication April 7, 2008.

Non-symbiotic 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 a nshb gene (cerhb) from the moss Ceratodon purpureus. Sequence analysis showed that cerhb is interrupted by three introns in identical position as all known plant nshb genes, which suggests that the ancestral nshb gene was interrupted by three 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 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 Lba structures revealed that the major evolutionary changes that probably occurred during the evolution of plant Hbs were (i) a hexacoordinate to pentacoordinate transition at the heme prosthetic group, (ii) a length decrease at the CD-loop and N- and C-termini regions, and (iii) the compaction of the protein into a globular structure.

Key Words: Ceratodon • evolution • gene expression • globin • molecular modeling • non-symbiotic


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