Abstract
In wheat root apices, aluminum (Al) activates ALMT1 to export malate. To elucidate the activation mechanism by Al, we compared the function and the amino-acid sequences of the ALMT1 of wheat, rye and Arabidopsis to identify the amino acid residues involved in the activation of ALMT1. Cultured tobacco cells were transformed with rye orthologs which exhibited 90% identity with wheat ALMT. The transformants which highly expressed rye ALMT1 gene released malate in response to Al as much as the transformants with wheat ALMT1. Furthermore, it has been reported that the ALMT1 ortholog of Arabidopsis (50% identity with wheat ALMT1) functions as Al-activated malate transporter. We hypothesized that the negatively-charged amino acids (Asp, Glu) interact with Al ion, and found several negatively-charged amino-acid residues conserved among these ALMT1 proteins. A malate efflux capability will be investigated in transgenic tobacco cells expressing the mutagenized ALMT1 proteins which are substituted these amino-acid residues.
