Proton exudation mediated by GmVP2 has widespread effects on plant growth, remobilization of soil phosphorus, and the structure of the rhizosphere microbial community.

ABSTRACT

Increased root secretion of H+ is a known strategy in plant adaption to low phosphorus (P) stress as it enhances mobilization of sparingly soluble P sources in the soil. However, our knowledge of the full effects induced by this enhanced acidification of the rhizosphere remains incomplete. In this study we found that P deficiency increased the net H+ flux rate from soybean (Glycine max) roots. Among the eight H+-pyrophosphatase (GmVP) genes in the soybean genome, GmVP2 showed the highest expression level under low P conditions. Transient expression of a GmVP2-GFP construct in tobacco (Nicotiana tabacum) leaves, together with functional characterization of GmVP2 in transgenic soybean hairy roots demonstrated that it encodes a plasma-membrane transporter that mediates H+ exudation. Overexpression of GmVP2 in Arabidopsis resulted in enhanced root H+ exudation, promoted root growth, and improved the utilization of sparingly soluble Ca-P. The improved root growth caused by GmVP2-overexpression might be due to the differential expression of genes related to hormone and flavonoid metabolism, and to root development. Overexpression of GmVP2 also changed the structure of the rhizospheric microbial community, as reflected by a preferential accumulation of Acidobacteria. Overall, our results suggest that GmVP2 mediates H+ exudation in the root response to Pi starvation, and that this influences plant growth, the mobilization sparingly soluble P-sources, and the structure of the microbial community in a coordinated manner.