The complex molecular basis of enhanced stress resilience in extreme drought-tolerant Arabis grassland species

Background and Aims

Plant species in competitive meadows must tolerate extreme stress, yet the mechanisms underlying resilience remain poorly understood. Arabis nemorensis , an endangered selfing species of Euro- pean floodplain grasslands, experiences both flooding and drought and hybridizes with its close relative, A. sagittata . We investigated how these species differ in drought survival and the molec- ular basis of their responses.

Methods

Sympatric lineages of A. nemorensis and A. sagittata were compared in a controlled dry-down experiment, complemented by transcriptome and small RNA profiling, and machine-learning anal- ysis of cis-regulatory motifs.

Key Results

Both species wilted at 5% soil moisture, but A. sagittata recovered more effectively (90% vs. 50%). This difference was not explained by a major QTL, suggesting a polygenic basis. Transcrip- tome profiling revealed stronger induction in A. sagittata (6,359 vs. 5,571 differentially expressed genes). Small RNA analysis identified species-specific regulation of miR408, a conserved drought regulator. Machine-learning identified 307 sequence motifs predictive of stress-responsive expres- sion, with motif distributions indicating distinct regulatory networks.

Conclusions

This study reveals the polygenic and regulatory complexity underlying divergent drought resili- ence strategies in the closely related species thriving in grassland environments.

Arabis nemorensis and its close relative A. sagittata co-occur in a floodplain meadow exposed to flooding and drought. In dry-down experiments, A. sagittata recovered more effectively than A. nemorensis . Transcriptome and small RNA analyses revealed stronger stress responses in A. sagittata , including regulation of miR408. These differences result from different regulatory networks and have a polygenic basis.