Rice (Oryza) hemoglobins

Abstract

Hemoglobins (Hbs) corresponding to non-symbiotic (nsHb) and truncated (tHb) Hbs have been identified in rice ( Oryza). This review discusses the major findings from the current studies on rice Hbs. At the molecular level, a family of the nshb genes, consisting of hb1, hb2, hb3, hb4 and hb5, and a single copy of the thb gene exist in Oryza sativa var. indica and O. sativa var. japonica, Hb 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 2, whereas rice Hb5 and tHb possibly exhibit a low to moderate affinity for O 2. 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 2-transport, O 2-sensing, NO-scavenging and redox-signaling. From an evolutionary perspective, an outline for the evolution of rice Hbs is available. Rice nshb and thb genes vertically evolved through different lineages, rice nsHbs evolved into clade I and clade II lineages and rice nshbs and thbs evolved under the effect of 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 cis-elements and trans-acting factors that regulate the expression of rice hb genes, and the partial understanding of the evolution of rice Hbs.

Rice phytoglobins regulate responses under low mineral nutrients and abiotic stresses in Arabidopsis thaliana

“…It has been known that rice Pgb genes code for Hb polypeptides of approximately 16‐ to 19‐kDa molecular mass (Arredondo‐Peter et al, ). Multiple sequence alignment of rice and Arabidopsis Pgs confirmed the presence of highly conserved distal and proximal histidine (His), phenylalanine (Phe), and proline (Pro) residues (Figure S2).…”

“…Plant Pgbs are known to be differentially expressed under various stresses, such as, hypoxia, nutrient deprivation, osmotic, cold, oxidative, and nitro‐sative stress (Arredondo‐Peter, Moran & Sarath, ; Mira et al, ; Mira, El‐Khateeb, Sayed Ahmed, Hill, & Stasolla, ). The recent reverse genetic approaches on Pgbs in Arabidopsis thaliana have emphasized their paramount role during plant growth and development by demonstrating that at least one functional Pgb gene is necessary for survival of young seedlings (Hebelstrup, Shah, & Igamberdiev, ; Hill, ).…”

“…The Pgb gene family in rice ( Oryza sativa ) has five members, OsPgb1.1 to 1.5 (Arredondo‐Peter et al, ). Previous microarray expression analysis has revealed differential expression of OsPgb1.1 and OsPgb1.2 under low K + and calcium (Ca 2+ ) (Shankar et al, , ) and abiotic stress conditions (Bai et al, ).…”

Effect of the synthesis of rice non-symbiotic hemoglobins 1 and 2 in the recombinant Escherichia coli TB1 growth

“…Five copies ( hb1 to 5 ) of the nshb gene have been detected in the rice genome, which are differentially expressed in embryonic and vegetative organs from plants growing under normal and stress conditions 8 – 11 . Based on the available information on the properties of rice nsHbs and data from the analysis of other plant and non-plant Hbs, it was proposed that rice nsHbs could exhibit a variety of functions in vivo , including O 2 -transport, O 2 -sensing, NO-scavenging and redox-signaling 6 , 12 , 13 . However, the in vivo activity of rice nsHbs has been poorly analyzed 12 .…”

“…Based on the available information on the properties of rice nsHbs and data from the analysis of other plant and non-plant Hbs, it was proposed that rice nsHbs could exhibit a variety of functions in vivo , including O 2 -transport, O 2 -sensing, NO-scavenging and redox-signaling 6 , 12 , 13 . However, the in vivo activity of rice nsHbs has been poorly analyzed 12 . An in vivo analysis for rice nsHbs is essential to elucidate the biological function(s) of these proteins.…”