Cistanthe longiscapa exhibits ecophysiological and molecular adaptations to the arid environments of the Atacama Desert.

This article focuses on the ecophysiological and transcriptomic analysis of *Cistanthe longiscapa*, an annual plant native to the Atacama Desert, to understand its adaptation and resilience to extreme aridity through crassulacean acid metabolism (CAM) photosynthesis. By sampling plants from three sites with varying precipitation levels, the study reveals significant intraspecific variation in CAM intensity, leaf succulence, isotopic carbon ratios, and gene expression profiles related to photosynthesis, stress response, and circadian regulation. Transcriptomic comparisons highlight site-specific molecular strategies, with stronger CAM activity and stress-related gene expression in the driest site, and enhanced photosynthetic and nitrogen assimilation processes in the less arid site. These findings position *C. longiscapa* as a valuable model for identifying genes involved in CAM modulation and drought tolerance, offering insights relevant to plant adaptation under climate change and potential crop improvement.