Abstract
Transmembrane transport of plant hormones is required for plant growth and development. Despite reports of a number of proteins that can transport the plant hormone gibberellin (GA), the mechanistic basis for GA transport and the identities of the transporters involved remain incomplete. Here, we provide evidence that Arabidopsis SWEET proteins, AtSWEET13 and AtSWEET14, which are members of a family that had previously been linked to sugar transport, are able to mediate cellular GA uptake when expressed in yeast and oocytes. A double sweet13 sweet14 mutant has a defect in anther dehiscence and this phenotype can be reversed by exogenous GA treatment. In addition, sweet13 sweet14 exhibits altered long distant transport of exogenously applied GA and altered responses to GA during germination and seedling stages. These results suggest that AtSWEET13 and AtSWEET14 may be involved in modulating GA response in Arabidopsis.
Highlights
Transmembrane transport of plant hormones is required for plant growth and development
AtNPF6.3 was originally identified as a dual affinity nitrate transporter CHL1/NRT1.1 that is regulated by protein phosphorylation[12,13]; AtNPF6.3/CHL1/NRT1.1 reportedly transports IAA with competition between nitrate and IAA playing an important role in lateral root development[14]
AtNPF2.10/GTR1 was identified as a gene that is co-expressed with jasmonate biosynthesis genes[18]
Summary
As predicted from yeast growth on selection media, AtSWEET14 promoted BD-GID1a/AD-GAI interactions more efficiently than did the other AtSWEETs, and 10 nM GA3 was sufficient to induce detectable b-gal activity. In the buffer conditions used previously for AtNPFs (50 mM potassium phosphate buffer, pH 5.8–7.0)[16,17,38], we were unable to detect significant GA transport activities by AtSWEET13 and AtSWEET14 in yeast (Supplementary Fig. 2a). We found that a significant amount of GA3 was taken into yeast expressing AtSWEET13 or AtSWEET14 when 100 mM glucose was added to the reaction buffer at acidic pH conditions (Fig. 2a; Supplementary Fig. 2a) This phenomenon appeared not to be direct regulation of AtSWEET13 and AtSWEET14 by glucose because similar induction of GA transport activity was observed for AtNPF2.5 that was previously shown to induce BD-GID1a/AD-GAI interactions in yeast[17] (Supplementary Fig. 2b). GA3 uptake into cells mediated by AtSWEET14 was saturated rapidly between 2.5 and 5 min (Supplementary Fig. 2d), and it pmol per oocyte Control AtSWEET13 AtSWEET14
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