In S. cerevisiae, borate resistance is mediated by the borate transport protein Bor1p. In plants, the role of borate transport is more complicated given the organism’s need to prevent borate toxicity while maintaining high enough levels of borate as a micronutrient that supports growth. As a result of these complex needs, the borate transporter family has expanded in plants, with seven borate transporters in Arabidopsis thaliana and four borate transporters in Oryza sativa. In humans, the transporter SLC4A11 has been suggested to transport borate, but this claim remains controversial. To better understand the transport activities of purported borate transporters, we tested the ability of eleven plant transporters and one human transporter to complement a BOR1 deletion in S. cerevisiae. We show that AtBor4, AtBor5, Atbor7, and OsBor3, can each complement yeast BOR1, while the other seven plant transporters do not. Interestingly, mapping these results onto phylogenetic analyses revealing two known clades within the borate transporter family might shed light on their functional and evolutionary differences. Next, we tested whether the ability to complement in yeast could be explained by the identity of the protein’s two domains, the Core and the Gate, by creating chimeric constructs combining the Core and Gate domains of AtBor1 and AtBor4. Our data show that neither chimeric construct complements, and thus the ability to complement arises synergistically from elements present in both domains rather than those that lie within just one protein domain. Lastly, we show that human SLC4A11 does not support borate transport in yeast, supporting claims that its transported substrate is not borate.
Support or Funding Information
Research reported in this study was supported by the National Institute Of General Medical Sciences of the National Institutes of Health under Award Number R15GM132786.
