Cork oak aquaporins: functional diversity and regulation with insights into drought response

Cork oak aquaporins exhibit diverse functional roles in water and solute transport, coordinating tissue-specific and drought-responsive mechanisms that regulate plant water balance and enhance adaptation to increasing climate-driven water scarcity. Cork oak woodlands are increasingly exposed to water scarcity due to climate change. At the cellular level, aquaporins (AQPs) regulate water and solute transport, yet their roles in cork oak remain largely unexplored. To bridge this knowledge gap, we examined the functional diversity, tissue localization, and drought response of cork oak AQPs and their contribution to plant water relations under stress. Four cork oak AQPs, QsPIP2;4, QsTIP2;1, QsNIP1;2, and QsNIP6;1, were expressed in Saccharomyces cerevisiae to characterize their functional properties. Stopped-flow spectroscopy showed that QsPIP2;4, QsTIP2;1, and QsNIP1;2 transport water, while QsNIPs facilitate glycerol permeability. Mercury chloride unexpectedly activated QsPIP2;4, an effect abolished in the C69A mutant, highlighting the role of Cys-69 in mercury binding and channel regulation. Yeast growth assays showed that QsNIP6;1 transports boron, hydrogen peroxide, and arsenic, suggesting broader physiological functions of cork AQPs. At the tissue level, immunolocalization showed widespread AQPs' accumulation across multiple tissue layers of young stems. Higher PIP2s abundance suggests they are likely the main contributors to water transport in these tissues. QsAQPs expression under mild drought stress showed that PIP and TIP were upregulated in leaves and stems, supporting their role in water homeostasis, whereas their downregulation in roots suggests a strategy to restrict water loss back to drying soils. Together, these results provide the first comprehensive molecular, functional, and physiological characterization of cork oak AQPs. They demonstrate how distinct AQPs coordinate water and solute transport under drought, advancing the understanding of cork oak water relations under extreme climatic conditions.