MtNIP5;1, a novel Medicago truncatula boron diffusion facilitator induced under deficiency

Abstract

Background: Boron (B) deficiency or toxicity in soils can cause the inhibition of growth and an altered development in plants. In such conditions, the participation of two distinct protein families (the aquaporin family Major intrinsic proteins (MIPs) and the Boron transporter family BOR) is required to minimize detrimental effects caused by B stress. Legumes comprise important crops that offer major agronomic benefits, including the capacity of establishing symbiosis with rhizobia fixing atmospheric N2 and for being important food protein sources. It has been proven that legumes are susceptible to B stress, which leads to important yield penalties. However, little is known about the transport mechanisms responsible for B uptake and distribution in legumes, especially under deficiency.Results: A Medicago truncatula protein, MtNIP5;1 (Medtr1g097840) (homologous to the Arabidopsis thaliana AtNIP5;1) was identified as a novel legume B transporter involved in B uptake under deficiency. Further analyses revealed that this M. truncatula aquaporin expression was boron-regulated in roots, being induced under deficiency and repressed under toxicity. It localizes at the plasma membrane of root epidermal cells and in nodules, where B plays pivotal roles in symbiosis. Furthermore, a partial complementation of the nip5;1 A. thaliana mutant phenotype under B deficiency supports a functional role of MtNIP5;1 as a B transporter in this legume model plant. Conclusions: The results here presented support a functional role of MtNIP5;1 in B uptake under deficiency and provides new insights into this micronutrient transport mechanisms in legume species.