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Two hemoglobin genes in Arabidopsis thaliana: the evolutionary origins of leghemoglobins

Trevaskis, B., Watts, R.A., Andersson, C.R., Llewellyn, D.J., Hargrove, M.S., Olson, J.S., Dennis, E.S., Peacock, W.J.
Proceedings of the National Academy of Sciences of the United States of America 1997 v.94 no.22 pp. 12230-12234
Arabidopsis thaliana, interspecific variation, messenger RNA, structural genes, complementary DNA, recombinant proteins, hemoglobin, cold stress, amino acid sequences, gene expression, water stress, oxygen, introns, roots, leaves
We cloned two hemoglobin genes from Arabidopsis thaliana. One gene, AHB1, is related in sequence to the family of non symbiotic hemoglobin genes previously identified in a number of plant species (class 1). The second hemoglobin gene, AHB2, represents a class of nonsymbiotic hemoglobin (class 2) related in sequence to the symbiotic hemoglobin genes of legumes and Casuarina. The properties of these two hemoglobins suggest that the two families of nonsymbiotic hemoglobins may differ in function from each other and from the symbiotic hemoglobins. AHB1 is induced, in both roots and rosette leaves, by low oxygen levels. Recombinant AHB1 has an oxygen affinity so high as to make it unlikely to function as an oxygen transporter. AHB2 is expressed at a low level in rosette leaves and is low temperature-inducible. AHB2 protein has a lower affinity for oxygen than AHB1 but is similar to AHB1 in having an unusually low, pH-sensitive oxygen off-rate.