Abstract
Copiapoa solaris is an endemic cactus species from the Antofagasta region, Chile, thriving in arid coastal ecosystems known as "fog oases," where the rising marine moisture is the primary water source. This study investigates the role of microbial communities associated with the rhizosphere of C. solaris in adapting to extreme environmental conditions, particularly focusing on the acdS gene, which encodes ACC deaminase-an enzyme that reduces ethylene production under stress. This research aims to elucidate the gene's contribution to the adaptation of C. solaris in these challenging environments. Samples were collected from three sites (El Cobre, Quebrada Botija, and Quebrada Izcuña) that differ in relative humidity, temperature, and topography. Environmental DNA was extracted, phylogenetic diversity was analyzed, and metagenomic annotation of the acdS gene was conducted. The acdS gene was detected in all samples, with the highest relative abundance at Quebrada Izcuña (0.05%), characterized by low relative humidity (<70%) and severe water stress. Phylogenetic analysis revealed conserved sequences across sites, while taxonomic and alpha diversity were similar among them. However, beta diversity indicated that Quebrada Izcuña was the least homogeneous, hosting distinct taxa potentially associated with stress mitigation. The acdS gene was detected on plasmids at El Cobre and Quebrada Izcuña, suggesting its potential mobility within the metagenome. The results of this study highlight the intricate relationships between microbial communities and the resilient cactus species C. solaris in extreme environments. The conservation and abundance of the acdS gene, particularly in low-humidity conditions, suggest its vital role in facilitating stress tolerance through microbial interactions. Understanding these dynamics is crucial for developing strategies to enhance plant resilience in arid ecosystems, with potential applications in sustainable agriculture and ecosystem management under changing climatic conditions.