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An extracellular hydrophilic carboxy‐terminal domain regulates the activity of TaALMT1, the aluminum‐activated malate transport protein of wheat
Author(s) -
Furuichi Takuya,
Sasaki Takayuki,
Tsuchiya Yoshiyuki,
Ryan Peter R.,
Delhaize Emmanuel,
Yamamoto Yoko
Publication year - 2010
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2010.04309.x
Subject(s) - terminal (telecommunication) , extracellular , microbiology and biotechnology , chemistry , biochemistry , c terminus , biophysics , biology , amino acid , computer science , telecommunications
Summary Al 3+ ‐resistant cultivars of wheat ( Triticum aestivum L.) release malate through the Al 3+ ‐activated anion transport protein Triticum aestivum aluminum‐activated malate transporter 1 (TaALMT1). Expression of TaALMT1 in Xenopus oocytes and tobacco suspension cells enhances the basal transport activity (inward and outward currents present in the absence of external Al 3+ ), and generates the same Al 3+ ‐activated currents (reflecting the Al 3+ ‐dependent transport function) as observed in wheat cells. We investigated the amino acid residues involved in this Al 3+ ‐dependent transport activity by generating a series of mutations to the TaALMT1 protein. We targeted the acidic residues on the hydrophilic C‐terminal domain of TaALMT1 and changed them to uncharged residues by site‐directed mutagenesis. These mutant proteins were expressed in Xenopus oocytes and their transport activity was measured before and after Al 3+ addition. Three mutations (E274Q, D275N and E284Q) abolished the Al 3+ ‐activated transport activity without affecting the basal transport activity. Truncation of the hydrophilic C‐terminal domain abolished both basal and Al 3+ ‐activated transport activities. Al 3+ ‐dependent transport activity was recovered by fusing the N‐terminal region of TaALMT1 with the C‐terminal region of AtALMT1, a homolog from Arabidopsis. These findings demonstrate that the extracellular C‐terminal domain is required for both basal and Al 3+ ‐dependent TaALMT1 activity. Furthermore, we identified three acidic amino acids within this domain that are specifically required for the activation of transport function by external Al 3+ .