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Identification of an abscisic acid transporter by functional screening using the receptor complex as a sensor

Kanno, Yuri, Hanada, Atsushi, Chiba, Yasutaka, Ichikawa, Takanari, Nakazawa, Miki, Matsui, Minami, Koshiba, Tomokazu, Kamiya, Yuji, Seo, Mitsunori
Proceedings of the National Academy of Sciences of the United States of America 2012 v.109 no.24 pp. 9653-9658
Arabidopsis, abscisic acid, biosynthesis, complementary DNA, gene overexpression, hypersensitivity, insects, leaves, mutants, nitrates, roots, screening, seed germination, stems, stomata, stomatal movement, surface temperature, two hybrid system techniques, vascular tissues, yeasts
Movement of the plant hormone abscisic acid (ABA) within plants has been documented; however, the molecular mechanisms that regulate ABA transport are not fully understood. By using a modified yeast two-hybrid system, we screened Arabidopsis cDNAs capable of inducing interactions between the ABA receptor PYR/PYL/RCAR and PP2C protein phosphatase under low ABA concentrations. By using this approach, we identified four members of the NRT1/PTR family as candidates for ABA importers. Transport assays in yeast and insect cells demonstrated that at least one of the candidates ABA-IMPORTING TRANSPORTER (AIT) 1, which had been characterized as the low-affinity nitrate transporter NRT1.2, mediates cellular ABA uptake. Compared with WT, the ait1 / nrt1 . 2 mutants were less sensitive to exogenously applied ABA during seed germination and/or postgermination growth, whereas overexpression of AIT1 / NRT1 . 2 resulted in ABA hypersensitivity in the same conditions. Interestingly, the inflorescence stems of ait1 / nrt1 . 2 had a lower surface temperature than those of the WT because of excess water loss from open stomata. We detected promoter activities of AIT1 / NRT1 . 2 around vascular tissues in inflorescence stems, leaves, and roots. These data suggest that the function of AIT1 / NRT1 . 2 as an ABA importer at the site of ABA biosynthesis is important for the regulation of stomatal aperture in inflorescence stems.