**5. Conclusions and Perspectives**

The implication of SULTRs in seed P accumulation not only provides novel opportunities to design routes for the breading of new *lpa* varieties in important cereal crops but also reveals the existence of a complex network of interactions between S and P homeostasis. The recent finding showing the involvement of *SULTR3;4*/*SPTDs* in delivering phosphate, and not sulfate, to developing tissues opens new questions about the nature of the other members of the SULTR3 subfamily [32,33]. Further investigations aimed at determining their substrate preference between sulfate and phosphate are then essential to unveil the actual role of these transporters in the control of nutrient homeostasis. In this context, the recent study of Cao et al. [29], suggesting that all the Arabidopsis *SULTR3* homologs may redundantly mediate sulfate import into the chloroplast, needs to be carefully reconsidered since chloroplasts isolated from the *sultr3* quintuple mutant retain about 50% of the sulfate uptake capacity of the wild type. Redundancy versus diversity will be the novel challenge to face.

**Author Contributions:** G.A.S. and F.F.N. equally contributed in discussing this opinion. F.F.N. wrote the manuscript. G.A.S. and F.F.N. revised and approved the final version of the opinion.

**Funding:** This work received no external funding.

**Acknowledgments:** The music of Gustav Mahler's V Symphony inspired this work. We would like to thank Maurizio Cocucci and Silvia Morgutti for their precious support during the writing of the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
