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 Brassicaceae 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 genetic adaptations that could facilitate an extremophyte lifestyle: (i) We identified positively selected genes indicative of common selective pressures in different extreme environments that target stomatal opening, nutrient acquisition, and UV-B induced DNA repair. In A. hierochuntica, we specifically identified genes consistent with a photoperiod-insensitive, early flowering phenotype that could be advantageous 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 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 and higher heat-induced fold-change expression than A. thaliana. We suggest that these transcriptome features are related to specific conditions native to a desert environment.