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Numerous studies suggest a relevant role of cytokinin (CK) distribution in shaping of plant morphology upon changing environment. Nonetheless, our knowledge about an involvement of short-distance CK translocation in root mineral nutrition is still scarce and specific role of CK transporters in root morphology has yet to be established. Revealing the molecular identity of CK transporters is thereby crucial for better understanding of root plasticity during soil fertility, as well as more frequently encountered plant nutrients deficiencies. In this work, we identified and characterized theMedicago truncatulafull-size ATP-binding cassette (ABC) transporter belonging to the G subfamily, namely MtABCG40 as a CK importer. Its expression is root-specific and is induced by nitrogen deprivation and CKs. Our analyses indicate that MtABCG40 has a negative impact on lateral root density through decreased lateral root initiation and enhancement of primary root elongation. Moreover, in line with postulated resemblance to lateral roots, we also observed an inhibitory influence of this transporter on nodule number. Our results suggest that MtABCG40 action affects CK signaling which impacts on the cellular response to auxin. We present data that demonstrate a full-size ABCG transporter with a novel function in legumes and CK transport.

SUMMARYNitrogen (N) as well as Phosphorus (P) are key nutrients determining crop productivity. Legumes have developed strategies to overcome nutrient limitation by e.g., forming a symbiotic relationship with N-fixing rhizobia and the release of P-mobilizing exudates and are thus able to grow without supply of N or P fertilizers. The legume-rhizobial symbiosis starts with root release of isoflavonoids, that act as signaling molecules perceived by compatible bacteria. Subsequently, bacteria release nod factors, which induce signaling cascades allowing the formation of functional N-fixing nodules.We report here the identification and functional characterization of a plasma membrane-localized MATE-type transporter (LaMATE2) involved in the release of genistein from white lupin roots.The LaMATE2 expression in the root is upregulated under N deficiency as well as low phosphate availability, two nutritional deficiencies that induce the release of this isoflavonoid. LaMATE2 silencing reduced genistein efflux and even more the formation of symbiotic nodules, supporting the crucial role of LaMATE2 in isoflavonoid release and nodulation. Furthermore, silencing of LaMATE2 limited the P-solubilization activity of lupin root exudates. Transport assays in yeast vesicles demonstrated that LaMATE2 acts as a proton-driven isoflavonoid transporter.