The aquaporin MePIP2;7 improves MeMGT9‐mediated Mg2+ acquisition in cassava

Abstract

AbstractAquaporins are important transmembrane water transport proteins which transport water and several neutral molecules. However, how aquaporins are involved in the synergistic transport of Mg2+ and water remains poorly understood. Here, we found that the cassava aquaporin MePIP2;7 was involved in Mg2+ transport through interaction with MeMGT9, a lower affinity magnesium transporter protein. Knockdown of MePIP2;7 in cassava led to magnesium deficiency in basal mature leaves with chlorosis and necrotic spots on their edges and starch over‐accumulation. Mg2+ content was significantly decreased in leaves and roots of MePIP2;7‐RNA interference (PIP‐Ri) plants grown in both field and Mg2+‐free hydroponic solution. Xenopus oocyte injection analysis verified that MePIP2;7 possessed the ability to transport water only and MeMGT9 was responsible for Mg2+ efflux. More importantly, MePIP2;7 improved the transportability of Mg2+ via MeMGT9 as verified using the CM66 mutant complementation assay and Xenopus oocytes expressing system. Yeast two‐hybrid, bimolecular fluorescence complementation, co‐localization, and co‐immunoprecipitation assays demonstrated the direct protein–protein interaction between MePIP2;7 and MeMGT9 in vivo. Mg2+ flux was significantly elevated in MePIP2;7‐overexpressing lines in hydroponic solution through non‐invasive micro‐test technique analysis. Under Mg2+‐free condition, the retarded growth of PIP‐Ri transgenic plants could be recovered with Mg2+ supplementation. Taken together, our results demonstrated the synergistic effect of the MePIP2;7 and MeMGT9 interaction in regulating water and Mg2+ absorption and transport in cassava.