Positive Selection and Heat-Response Transcriptomes Reveal Adaptive Features of the Arabidopsis Desert Relative, Anastatica hierochuntica

Extremophytes have evolved genetic adaptations for tolerance to abiotic stresses characteristic of their extreme environments. Comparative molecular analyses of Arabidopsis thaliana with its halophytic extremophyte relatives have revealed that the halophytes exist in a pre-adapted, stress-ready state. We generated a reference transcriptome of the heat-tolerant A. thaliana desert relative, Anastatica hierochuntica (True Rose of Jericho) and used two approaches to identify adaptations that could facilitate an extremophyte lifestyle: (i) We identified common positively selected extremophyte genes that target stomatal opening, nutrient acquisition, and UV-B induced DNA repair. In A. hierochuntica , we identified genes consistent with a photoperiod-insensitive, early-flowering phenotype that could maximize fitness in the desert environment; (ii) Using RNA-seq analysis, we demonstrate that A. thaliana and A. hierochuntica transcriptomes exhibit similar transcriptional adjustment in response to heat, and that the A. hierochuntica transcriptome does not exist in a heat stress-ready state, unlike its halophytic relatives. Furthermore, the A. hierochuntica global transcriptome as well as orthologs belonging to specific functional groups, display a lower basal expression but higher heat-induced expression than in A. thaliana . We suggest that the increased reactiveness of the A. hierochuntica transcriptome in response to heat stress is related to specific conditions native to a desert environment. ### Competing Interest Statement The authors have declared no competing interest.