Identification of an abscisic acid transporter by functional screening using the receptor complex as a sensor.
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.
Plant Science Center, RIKEN, Yokohama, Kanagawa 230-0045,  Japan.
Yuri
Y
Kanno
Atsushi
A
Hanada
Yasutaka
Y
Chiba
Takanari
T
Ichikawa
Miki
M
Nakazawa
Minami
M
Matsui
Tomokazu
T
Koshiba
Yuji
Y
Kamiya
Mitsunori
M
Seo
D000040:Abscisic Acid / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D000040:Abscisic Acid