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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Plant Sci. | doi: 10.3389/fpls.2019.01121

A comprehensive biophysical model of ion and water transport in plant roots. II. Clarifying the roles of SOS1 in the salt stress response in Arabidopsis

  • 1University of South Australia, Phenomics and Bioinformatics Research Centre, School of Mathematics and Statistics, University of South Australia, Australia

SOS1 transporters play an essential role in plant salt tolerance. Although \textit{SOS1} is known to encode a plasma membrane Na$^+$/H$^+$ antiporter,
the transport mechanisms by which these transporters contribute to salt tolerance
at the level of the whole root are unclear. Gene expression and flux measurements have provided
conflicting evidence for the location of SOS1 transporter activity, making
it difficult to determine their function. Whether SOS1 transporters load
or unload Na$^+$ from the root xylem transpiration stream is also disputed.
To address these areas of contention, we applied a mathematical model to
answer the question: what is the function of SOS1 transporters in
salt-stressed Arabisopsis roots?

We used our biophysical model of ion and water transport in a
salt-stressed root to simulate a wide range of SOS1 transporter locations in
a model Arabidopsis root,
providing a level of detail that cannot currently be achieved by
experimentation. We compared our simulations with available experimental
data to find reasonable parameters for the model and to determine likely
locations of SOS1 transporter activity.

We found that SOS1 transporters are likely to be operating in at least one
tissue of the outer mature root, in the mature stele, and in the epidermis
of the root apex. SOS1 transporter activity in the mature outer root cells
is essential to maintain low cytosolic Na$^+$ levels in the root and also
restricts the uptake of Na$^+$ to the shoot. SOS1 transporters in the stele
actively load Na$^+$ into the xylem transpiration stream, enhancing the
transport of Na$^+$ and water to the shoot. SOS1 transporters acting in the
apex restrict cytosolic Na$^+$ concentrations in the apex, but are unable to
maintain low cytosolic Na$^+$ levels in the mature root.

Our findings suggest that targeted, tissue specific, overexpression or
knockout of \textit{SOS1} may lead to greater salt tolerance than has been achieved
with constitutive gene changes. Tissue-specific changes to the expression
of \textit{SOS1} could be used to identify the appropriate balance between limiting
Na$^+$ uptake to the shoot while maintaining water uptake, potentially
leading to enhancements in salt tolerance.

Keywords: Na+/H+ plasma membrane antiporter, Na+ transport, water transport, Arabidopsis, salt stress, Water stress, salt tolerance

Received: 12 Apr 2019; Accepted: 14 Aug 2019.

Copyright: © 2019 Miklavcic and Foster. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Stanley J. Miklavcic, Phenomics and Bioinformatics Research Centre, School of Mathematics and Statistics, University of South Australia, University of South Australia, Adelaide, Australia, Stan.Miklavcic@unisa.edu.au