Rice hemoglobins ( Oryza ) [

Hemoglobins (Hbs) corresponding to non-symbiotic (nsHb) and truncated (tHb) Hbs have been identified in rice ( ). This review discusses the major Oryza findings from the current studies on rice Hbs. At the molecular level, a family of the genes, consisting of , , , and , and a single copy of nshb hb1 hb2 hb3 hb4 hb5 the gene exist in var. indica and . var. japonica, Hb thb Oryza sativa O sativa transcripts coexist in rice organs and Hb polypeptides exist in rice embryonic and vegetative organs and in the cytoplasm of differentiating cells. At the structural level, the crystal structure of rice Hb1 has been elucidated, and the structures of the other rice Hbs have been modeled. Kinetic analysis indicated that rice Hb1 and 2, and possibly rice Hb3 and 4, exhibit an extremely high affinity for O , whereas rice Hb5 and tHb possibly exhibit a low to moderate affinity for O . Based on the accumulated information on the properties of rice Hbs and data from the analysis of other plant and non-plant Hbs, it is likely that Hbs play a variety of roles in rice organs, including O -transport, O -sensing, NO-scavenging and redox-signaling. From an evolutionary perspective, an outline for the evolution of rice Hbs is available. Rice and genes nshb thb vertically evolved through different lineages, rice nsHbs evolved into clade I and clade II lineages and rice s and s evolved under the effect of nshb thb neutral selection. This review also reveals lacunae in our ability to completely understand rice Hbs. Primary lacunae are the absence of experimental information about the precise functions of rice Hbs, the properties of modeled rice Hbs and the -elements and -acting factors that regulate the cis trans expression of rice genes, and the partial understanding of the evolution of hb rice Hbs. 1 2