Major concerns:
Title of this paper accurately reflect the results in most cases, alas, some results raised questions after reading the paper. In our first reading, the necessity of figure 1B was not clearly understood. It would be helpful to emphasize how unrelated MtZIP6 and GmZIP1 are from each other. They are highlighted in red in the figure, however, they are not commented in the figure legend. These are orthologs with similar functions, yet they do not group together in a tree based on sequence similarity.
We had concerns Figures 4 and 5 could have been combined into a single figure. They address the same finding, and side by side comparison of Figure 4B and 5A, as well as 4C and 5B, may have emphasized differences and consolidated figure legends. There were questions about the statistical significance of findings presented in Figure 4.
Regarding figure 6B, we are confused about what it is the message authors want to send. The figure supports the zinc-depend concentration of MtZIP6, but it was relatively difficult to understand the rationale to test different concentration of zinc. Since figure 6A showed that zinc concentration in WT nodules is lower compared to nodules in RNAi line, in figure 6C I was expecting to observe the same zinc concentration pattern shown in figure 6A. We wonder if the exposure times were changed during image acquisition to prevent oversaturation of the image.
In figure 7, uncharacterized transporters are denoted by question marks. We think it is helpful for the reader to be able to look at a summary model but the question marks in the suggested transporters might be misleading. After all, it is just a suggested model which summarizes what we know so far from studies in other species; it is obvious that further studies are needed to validate it. Some of the not yet characterized transporters were eliminated in the final publication, helping to streamline main findings.