Abstract EANA2026-256

Soil salinity restricts plant growth by disrupting ion homeostasis, cellular organization, and cytoskeletal dynamics. This study compared the salt-sensitive model plant Arabidopsis thaliana Col-0 with the extremophyte Schrenkiella parvula to determine how actin filaments and microtubules contribute to salt tolerance. Seedlings were exposed to 50–300 mM NaCl, and root growth, fresh biomass, and the expression of cytoskeleton-associated genes were evaluated. In a complementary pharmacological experiment, seven-day-old seedlings were treated for six days with 100 mM NaCl alone or in combination with 0.2 µM latrunculin B, an inhibitor of actin polymerization, or 1 µM oryzalin, a microtubule-disrupting agent. An independent International Space Station transcriptomic dataset was also examined to determine whether spaceflight modified cytoskeletal gene expression in S. parvula under salinity.

At 100 mM NaCl, day-six root length decreased by only 10.8% in A. thaliana and 2.0% in S. parvula. In contrast, latrunculin B and oryzalin reduced root length by 56.1% and 60.3% in A. thaliana, and by 36.4% and 42.7% in S. parvula, respectively. Combined inhibitor and salt treatments maintained strong growth inhibition, indicating that functional actin and microtubule networks are required for sustained root elongation. In A. thaliana, 200 mM NaCl strongly suppressed the expression of MAP65, SPR1, PHS1, RIC1, ROP2, WDL5, ACT7, and ACT8 to approximately 22–38% of control levels. By contrast, S. parvula showed increased expression of PHS1, RIC1, WDL5, ACT7, and ACT8 at 300 mM NaCl, reaching approximately 1.8- to 4.7-fold above control levels. Descriptive analysis of the ISS dataset further showed that, under 100 mM NaCl, S. parvula maintained higher transcript abundance of ACT7, ACT8, WDL5, SPR1, MAP65-1, and MAP65-6 in space than under the corresponding ground treatment. Under the same conditions, ROP2, RIC1, and PHS1 transcripts were detected in the spaceflight sample but not in the matched ground sample.

Together, these findings indicate that S. parvula sustains growth under salinity through more robust regulation of actin and microtubule-associated processes. The ISS observations further suggest that spaceflight modifies the interaction between salinity and cytoskeletal transcriptional responses.