The third member of the hemA gene family encoding glutamyl-tRNA reductase is primarily expressed in roots in Hordeum vulgare

Accumulation of chlorophylls and heme is primarily controlled at the level of 5-aminolevulinate (ALA) synthesis in higher plants. ALA is formed from glutamate in three enzymatic steps in plants. Among them, the reduction of glutamyl-tRNA(Glu) to glutamate-1-semialdehyde (GSA) is likely to be a regulatory point of ALA synthesis. This reaction is catalyzed by glutamyl-tRNA reductase (GTR), which is encoded by a hemA gene. We have isolated a novel isoform of a hemA cDNA clone from barley (Hordeum vulgare) that is the third member of the hemA gene family. mRNA of this isoform is accumulated primarily in roots, suggesting that the isoform is regulated in an organ-specific manner by the demand for heme synthesis rather than chlorophyll. Phylogenetic analysis was done using the deduced amino acid sequences of hemA isoforms from barley, cucumber and Arabidopsis thaliana. The results indicate that the existing gene families in these plants arose after the divergence of monocotyledonous and dicotyledonous plants.