Mycorrhizal symbiosis and water deficit: morphophysiological and gene expression responses in Caatinga passion fruit.

Abstract: The advancement of global warming and climate change requires strategic actions in understanding and seeking interactions between plant species and microorganisms that are more tolerant to water deficit. This research assessed the morpho-agronomic, physio- logical, and gene expression responses of two Passiflora cincinnata accessions (tolerant and sensitive) to water deficit, focusing on their relationship with mycorrhization. A random- ized design with two accessions, two field capacities, and four AMF inoculation treatments was used to compare drought and control conditions. Differential gene expression was analyzed under drought stress, and the effect of mycorrhization on stress tolerance was evaluated. The results showed that inoculation with native arbuscular mycorrhizal fungi (AMF) communities, especially those from water-deficit conditions (AMF25), resulted in greater increases in height, number of leaves, stem diameter, number of tendrils, leaf area, and fresh biomass of root and shoot, with increases ranging from 50% to 300% compared to the control (non-inoculated) and monospecific inoculation (Entrophospora etunicata). Higher photosynthetic rate and water use efficiency were observed in the tolerant accession. Myc- orrhizal inoculation increased the total chlorophyll content in both accessions, especially when inoculated with native AMF communities. Overall, P. cincinnata showed higher mycorrhizal responsiveness when inoculated with native AMF communities compared to monospecific inoculation with E. etunicata. The tolerant accession showed overexpression of the genes PcbZIP, PcSIP, and PcSTK, which are associated with signal transduction, water deficit tolerance, osmoregulation, and water transport. In contrast, the water deficit- sensitive accession showed repression of the PcSIP and PcSTK genes, indicating their potential use for distinguishing tolerant and sensitive accessions of the species. The toler- ance of P. cincinnata to water deficit is directly related to physiological responses, increased photosynthetic rate, efficient water use, and regulation of gene expression.