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

Non-symbiotic hemoglobins (nsHbs) are widely distributed in land plants, including rice. These proteins are classified into type 1 (nsHbs-1) and type 2. The O (2)-affinity of nsHbs-1 is very high mostly because of an extremely low O (2)-dissociation rate constant resulting in that nsHbs-1 apparently do not release O (2) after oxygenation. Thus, it is possible that the in vivo function of nsHbs-1 is other than O (2)-transport. Based on the properties of multiple Hbs it was proposed that nsHbs-1 could play diverse roles in rice organs, however the in vivo activity of rice nsHbs-1 has been poorly analyzed. An in vivo analysis for rice nsHbs-1 is essential to elucidate the biological function(s) of these proteins. Rice Hb1 and Hb2 are nsHbs-1 that have been generated in recombinant Es cherichia coli TB1. The rice Hb1 and Hb2 amino acid sequence, tertiary structure and rate and equilibrium constants for the reaction of O (2) are highly similar. Thus, it is possible that rice Hb1 and Hb2 function similarly in vivo. As an initial approach to test this hypothesis we analyzed the effect of the synthesis of rice Hb1 and Hb2 in the recombinant E. coli TB1 growth. Effect of the synthesis of the O (2)-carrying soybean leghemoglobin a, cowpea leghemoglobin II and Vitreoscilla Hb in the recombinant E. coli TB1 growth was also analyzed as an O (2)-carrier control. Our results showed that synthesis of rice Hb1, rice Hb2, soybean Lb a, cowpea LbII and Vitreoscilla Hb inhibits the recombinant E. coli TB1 growth and that growth inhibition was stronger when recombinant E. coli TB1 synthesized rice Hb2 than when synthesized rice Hb1. These results suggested that rice Hb1 and Hb2 could function differently in vivo.