Variability of non-symbiotic and truncated hemoglobin genes from the genome of cultivated monocots

Non-symbiotic (nsHb) and truncated (tHb) hemoglobins (Hbs) have been detected in a variety of land plants. The evolution of land plant nsHbs and tHbs at the protein level is well documented; however, little is known about the evolution of genes coding for these proteins. For example, the variability of the land plant nshb and thb genes is not known. Here, we report the variability of the nshb and thb genes from the genome of the cultivated monocots Brachypodium distachyon, Hordeum vulgare (barley), Oryza glaberrima (rice), O. rufipogon (rice), O. sativa (rice) var indica, O. sativa (rice) var japonica, Panicum virgatum (switchgrass), Setaria italica (foxtail millet), Sorghum bicolor (sorghum), Triticum aestivum (wheat), and Zea mays ssp. mays (maize) using sequence comparison and computational methods. Our results revealed that in cultivated monocots variability is higher in nshbs than in thbs, and suggest that major substitution events that occurred during the evolution of the cultivated monocot hbs were A→G and T→C transitions and that these genes evolved under the effect of neutral selection.