Climate change poses a direct threat to food security, with global warming leading to detrimental droughts that affect plant development and agricultural productivity. This study focused on the symbiotic relationship between plants and microorganisms, known for their pivotal role in plant adaptation to environmental stress. Strawberry plants ( Fragaria x ananassa) were inoculated with two endophytic fungi, Penicillium chrysogenum and Penicillium brevicompactum, isolated from Antarctic plants. Greenhouse experiments showed that inoculated plants had better water retention, photosynthesis, and reduced proline content and lipid peroxidation. Inoculation also boosted antioxidant activity and overall antioxidant capacity. Furthermore, a transcriptomics and cis element/transcription factor analysis revealed differentially expressed genes (DEGs) related to abscisic acid (ABA) signaling, such as dehydrins, and genes related to cellular water homeostasis such as aquaporins. The DEGs suggested an enhanced response to water stress, providing molecular insights of the potential mechanisms involved into the improved physiological performance of inoculated plants under drought and high-temperature conditions. The study underscores the importance of these molecular responses in establishing a resilient symbiotic relationship between plants and Antarctic microorganisms, offering promising avenues for further understanding and harnessing adaptive mechanisms to mitigate the impact of climate change on crop productivity.

Plants share their habitats with a multitude of different microbes. This close vicinity promoted the evolution of inter-organismic interactions between plants and many different microorganisms that provide mutual growth benefits both to the plant and the microbial partner. The symbiosis of Arabidopsis thaliana with the beneficial root colonizing endophyte Serendipita indica represents a well-studied system. Co-colonization of Arabidopsis roots with S. indica significantly promotes plant growth. Due to the notable phenotypic alterations of fungus-infected root systems, the involvement of a reprogramming of plant hormone levels, especially that of indole-3-acetic acid, has been suggested earlier. However, until now, the molecular mechanism by which S. indica promotes plant growth remains largely unknown. This study used comprehensive transcriptomics, metabolomics, reverse genetics, and life cell imaging to reveal the intricacies of auxin-related processes that affect root growth in the symbiosis between A. thaliana and S. indica. Our experiments revealed the essential role of tightly controlled auxin conjugation in the plant–fungus interaction. It particularly highlighted the importance of two GRETCHEN HAGEN 3 ( GH3) genes, GH3.5 and GH3.17, for the fungus infection-triggered stimulation of biomass production, thus broadening our knowledge about the function of GH3s in plants. Furthermore, we provide evidence for the transcriptional alteration of the PIN2 auxin transporter gene in roots of Arabidopsis seedlings infected with S. indica and demonstrate that this transcriptional adjustment affects auxin signaling in roots, which results in increased plant growth.