Characterizing Gibberellin Transport Activity by the NPF Family

The plant hormone gibberellin (GA) is fundamental for many aspects of plant growth and development. The best-known contribution of GA manipulations to agriculture is the introduction of dwarfing alleles into staple crops, which are one of the foundations of the "Green Revolution" that resulted in increased global wheat and rice yields. Movement of GA within plants has been documented and proven to be essential for proper plant growth, however little is known about the molecular mechanisms executing GA transport. We have recently identified NPF3 as the first bona fide GA transporter in plants. Other groups showed that additional Arabidopsis NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER family (NPF) members promote GA uptake in yeast, making the NPF proteins excellent candidates for further GA transport research. NPF transporters were first identified as nitrate transporters. There are 53 NPFs in Arabidopsis, divided into 8 functionally redundant subfamilies. In order to overcome functional redundancy and identify novel GA transporters, we combined GA response experiments with a multi-targeted amiRNA approach. We identified 2 novel members of the NPF family with the ability to transport GA in a Xenopus oocytes heterologous transport system. One protein can facilitate GA import while the other promotes GA export. These results provide the first evidence for GA export activity in plants. Accordingly, the individual mutant lines display an opposite GA mediated phenotype that is dependent on nitrate levels. By characterizing the biochemical activity and localization of the novel GA transporters discovered in this work we expect to shed light on the mechanisms governing GA transport and localization and expose the interplay between nitrate levels and GA response.