Functional characterization of betaine/proline transporters in betaine-accumulating mangrove.
Betaine is an important osmoprotectant in many plants, but its transport activity has only been demonstrated using a proline transporter from tomato, a betaine-nonaccumulating plant. In this study, two full-length and one partial transporter genes were isolated from betaine-accumulating mangrove Avicennia marina. Their homologies to betaine transporters from bacteria and betaine/4-aminobutyrate transporters from mammalian cells were low but were high to proline transporters from Arabidopsis and tomato. Two full-length transporters could complement the Na(+)-sensitive phenotype of the Escherichia coli mutant deficient in betT, putPA, proP, and proU. Both transporters could efficiently take up betaine and proline with similar affinities (K(m), 0.32-0.43 mm) and maximum velocities (1.9-3.6 nmol/min/mg of protein). The uptakes of betaine and proline were significantly inhibited by mono- and dimethylglycine but only partially inhibited by betaine aldehyde, choline, and 4-aminobutyrate. Sodium and potassium chloride markedly enhanced betaine uptake rates with optimum concentrations at 0.5 m, whereas sucrose showed only modest activation. The change of amino acids Thr(290)-Thr-Ser(292) in a putative periplasmic loop to Arg(290)-Gly-Arg(292) yielded the active transporter independent of salts, suggesting the positive charge induced a conformational change to the active form. These data clearly indicate that the betaine-accumulating mangrove contains betaine/proline transporters whose properties are distinct from betaine transporters of bacteria and mammalian cells.
Waditee
Rungaroon
R
Research Institute, Faculty of Science and Technology, and School of Agriculture, Meijo University, Nagoya 468-8502, Japan.
Hibino
Takashi
T
Tanaka
Yoshito
Y
Nakamura
Tatsunosuke
T
Incharoensakdi
Aran
A
Hayakawa
Shinsuke
S
Suzuki
Shigetoshi
S
Futsuhara
Yuzo
Y
Kawamitsu
Yoshinobu
Y
Takabe
Tetsuko
T
Takabe
Teruhiro
T
D000595:Amino Acid Sequence; D026921:Amino Acid Transport Systems, Neutral / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D001622:Betaine / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D050485:GABA Plasma Membrane Transport Proteins; D007700:Kinetics; D008969:Molecular Sequence Data; D011392:Proline / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014197:Trees / Q000378:metabolism*
D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; C072207:betaine plasma membrane transport proteins; D001622:Betaine; C033082:proline transporter; D011392:Proline