Birch gene activity offers clues to contrasting salt-stress responses

Salt tolerance is not simply a matter of switching more genes on. In a new study, the salt-tolerant birch species showed fewer changes in gene activity than its salt-sensitive relative. The researchers interpret this contrast as a possible clue to how plants already adapted to saline environments respond differently to a salt challenge.

The work, posted as a bioRxiv preprint on November 2, 2026, has not been certified by peer review. It compares Betula halophila, a salt-tolerant species, with Betula platyphylla, which the authors describe as having weak salt resistance. Its main contribution is a set of candidate genes and predicted regulatory relationships for future investigation.

Comparing a day of salt exposure

The researchers reanalyzed publicly available RNA-sequencing datasets from earlier studies. These covered leaves of B. halophila and both leaves and roots of B. platyphylla, with three biological replicates. They compared samples taken before treatment with samples exposed to 200 millimolar sodium chloride for 24 hours.

RNA sequencing measures the abundance of gene transcripts, providing a picture of gene activity. The team mapped the sequencing reads to a reference genome from another birch, B. pendula, then identified genes whose expression differed between the two sampling conditions.

They reported 956 differentially expressed genes in B. halophila leaves, compared with 2,955 in B. platyphylla leaves and 3,827 in its roots. Decreases outnumbered increases in the salt-tolerant species’ leaves; the reverse was true in both tissues of the salt-sensitive species.

The authors suggest that the smaller transcriptional response could reflect an existing capacity to maintain cellular balance under salty conditions. That remains an interpretation: the number of changing genes alone does not demonstrate the mechanism responsible for tolerance.

Cell walls connect the responses

Several clusters of gene-expression changes in B. halophila leaves resembled those in B. platyphylla roots. This was a similarity in selected expression patterns, not in the total number of affected genes.

Genes associated with cell-wall organization or formation were overrepresented among the changing genes in both of these tissue groups. Cell walls provide structural support, making their maintenance a relevant process to investigate during stress.

However, sharing a functional category did not mean responding identically. Many genes associated with cell-wall formation and wall-related proteins decreased in activity in B. halophila leaves, whereas they increased in B. platyphylla leaves and roots. The authors propose that these opposing responses may reflect different adjustment strategies. The expression analysis itself does not establish corresponding changes in wall structure or composition.

Hormone-related responses also differed. Changes in genes associated with hormone production, signaling and response occurred mainly in B. platyphylla. Although the authors discuss delayed hormonal responses as a possible explanation for the pattern in B. halophila, a comparison of baseline and 24-hour samples cannot establish the timing of such a delay.

Candidate regulators, not confirmed mechanisms

The team identified 121 genes whose expression changed in all three tissue groups. They used computational network inference to propose relationships among genes, and comparisons with known Arabidopsis genes to highlight candidates potentially involved in salt responses.

A separate experiment measured nine selected genes in B. platyphylla seedlings using RT-qPCR. After the same salt concentration and exposure duration, genes corresponding to RD26, ANAC2, HSFB2B and EDL3 increased in expression in both leaves and roots. GALS1 and KEA6 decreased in both tissues. MKK9, UXE1/MUR4 and HIS1-3 decreased in roots but increased in leaves.

These measurements support salt-responsive expression of the selected genes in B. platyphylla. They do not verify the predicted connections between genes or show that changing a candidate gene improves salt tolerance. The study reports expression measurements and inferred networks, rather than gene-manipulation experiments demonstrating improved survival or growth.

For breeding, the result is therefore a shortlist of leads. The comparison points toward both shared stress responses and species-specific adjustments, while leaving the causal basis of birch salt tolerance unresolved.