Functional Genomics of Salt Tolerance Mechanisms in Halophytic Plant Species
DOI:
https://doi.org/10.5281/zenodo.22688183Keywords:
halophyte, salt tolerance, Suaeda salsa, comparative transcriptomics, Na+/H+ antiporter, SOS pathway, ion homeostasisAbstract
Halophytes complete their life cycle at soil salinities that are lethal to most crop species, yet the genetic basis of
this tolerance is still incompletely resolved at the level of coordinated gene expression across tissues and salinity
regimes. We generated a comparative transcriptomic dataset for the euhalophyte Suaeda salsa and the
glycophytic reference Chenopodium quinoa cultivar Titicaca, grown hydroponically across a controlled salinity
gradient (0, 200, 400 and 600 mM NaCl) and sampled at root and shoot tissue after 72 hours of exposure. RNA
sequencing of 96 libraries identified 4,218 genes differentially expressed in S. salsa roots across the gradient,
more than twice the number detected in C. quinoa roots under the equivalent treatment, with the excess
concentrated in ion transport, vacuolar sequestration and osmolyte biosynthesis functional categories. Members
of the Salt Overly Sensitive (SOS) pathway, together with tonoplast Na+/H+ antiporter (NHX) and high-affinity
potassium transporter (HKT) gene families, showed constitutively elevated baseline expression in unstressed S.
salsa relative to C. quinoa, with comparatively modest further induction upon salt exposure, consistent with a
pre-adapted rather than purely inducible tolerance strategy. Ion content analysis showed S. salsa sequestered
sodium preferentially in shoot vacuoles, maintaining a shoot Na+/K+ ratio below 4 at 600 mM NaCl while C.
quinoa exceeded a ratio of 11 at the same treatment, and this partitioning correlated with tissue-specific NHX1
expression rather than with total NHX transcript abundance. Heterologous expression of the lead S. salsa NHX1
orthologue in a salt-sensitive yeast mutant partially restored growth under NaCl challenge, supporting a functional
role for the encoded transporter. These results identify constitutive, rather than salt-induced, expression of
ion-homeostasis genes as a defining transcriptional signature of euhalophyte tolerance and nominate specific
NHX and HKT paralogues as candidates for testing in glycophytic crop backgrounds.
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