Molecular cloning and characterization of cDNAs encoding hemoglobin from wheat (Triticum aestivum) and potato (Solanum tuberosum).

Hemoglobins (Hbs) are heme proteins encountered in all five kingdoms of living organisms. In plants, two different classes of Hbs have been identified: nonsymbiotic (class I) from both monocot and dicot species and symbiotic (class II) Hbs from nitrogen-fixing plants. This work reports the cloning and analysis of three nonsymbiotic Hb genes from wheat (Triticum aestivum) and potato (Solanum tuberosum). The Hb cDNAs were amplified by reverse transcriptase polymerase chain reaction (RT-PCR) using consensus oligonucleotide primers for nonsymbiotic Hbs.A wheat Hb cDNA (TaHb1) was isolated and shows a very high similarity to nonsymbiotic Hbs from Hordeum vulgare (98%) and Zea mays (83%). Another wheat Hb cDNA, designated TaHb2, exhibited strong similarity to truncated bacterial Hbs, the so-called 2-on-2 Hbs. In addition, a third Hb was cloned from potato, StHb. Expression analysis by RT-PCR demonstrated a very high expression level of the TaHb1 gene only in wheat roots. In contrast, the other wheat hemoglobin gene, TaHb2, was demonstrated to be constitutively expressed although differences in expression level in different tissues were observed. The expression of the TaHb1 gene is induced in wheat roots exposed to microaerobic conditions. The potato Hb gene, StHb, was highly expressed in roots and also in tubers and stem tissue although at much reduced levels.