Poster: Salinity

Abs # 154: Functional characterization of betaine/proline transporters in betaine accumulating

Presenter:	Tanaka, Yoshito , ytanaka@ccmfs.meijo-u.ac.jp
Authors	Tanaka, Yoshito  (A)   Waditee, Rungaroon  (A)   Takabe, Tetsuko  (B)   Nakamura, Tetsunosuke  (C)   Takabe, Teruhiro  (A)
Affiliations:	(A): Meijo University (B): Nagoya University (C): Niigata University of Pharmacy and Applied Life Sciences

Betaine is an important osmoprotectant in many plants, but its transport activity has only been demonstrated using a proline transporter (LeProT) from tomato, a betaine non accumulating plant. Among three LeProTs, only LeProT1 was specifically expressed in pollen whereas the mRNA for LeProT2 and LeProT3 could not be detected in any organs. It was shown that LeProT1 could take up proline, betaine, and 4-aminobutyrate (GABA). 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/GABA transporters from mammalian cells were low, but high to proline transporters from Arabidopsis and tomato. Two full length transporters could complement the Na⁺-sensitive phenotype of the E. coli mutant deficient in betT, putPA, proP, and proU. Both transporters could efficiently take up betaine and proline with similar affinities (Km, 0.32-0.43 mM) and maximum velocities (1.9-3.6 nmol/min mg protein). The uptakes of betaine and proline were significantly inhibited by mono- and di-methylglycine, but only partially inhibited by betaine aldehyde, choline, and GABA. 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 290Thr-Thr-Ser292 in a putative periplasmic loop to 290Arg-Gly-Arg292 yielded the active transporter independent of salts, suggesting the positive charge induced conformational change to 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.