These figures clearly help to prove the point that MtZIP6 has some important function in the development of healthy symbiosis as supported by results about the number of red(functional) and white(nonfunctional) nodules, dry weight and Acetylene reduction assay. But we think that these two figures can be combined together and this will help to provide a better view of the overall picture about the vital need of MtZIP6. This would also have provided space to include the tobacco results into the main paper instead of supplemental.
In figure 7 the authors present a proposed model to summarize their findings and their hypothesis for zinc uptake by nodule cells. The model fits their results, which showed that ZIP6 is most probably localized in the cell membrane of the differentiation cells and that knockdown of ZIP6 plants accumulate zinc in the apoplastic regions. So, suggesting that ZIP6 is responsible for transporting zinc inside cells infected with rhizobia seems like a plausible conclusion. In this model, the authors attempt also to fill in other missing pieces of the zinc uptake pathway in nodules. Uncharacterized transporters are denoted by question marks. I think it is helpful for the reader to include a summary model but the question marks in the suggested transporters might be confusing. 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.
Figure 6c and d aimed to show the differences in zinc accumulation in a WT nodule compared to the MtZIP6 RNAi knockdown. It was stated that higher accumulation occurred in the differentiation zone of the mutant nodule. However, the images gave a differing impression. It is clear that the zinc does not disperse into the rest of the nodule and remains in the differentiation zone, but a higher zinc accumulation compared to WT nodule is not clear. Perhaps it should be noted in the figure legend that fig. 6d had been altered in order to avoid oversaturation in the image.