Expression Analysis of Aquaporins from Desert Truffle Mycorrhizal Symbiosis Reveals a Fine-Tuned Regulation Under Drought

We have performed the isolation, functional characteriza- tion, and expression analysis of aquaporins in roots and leaves of Helianthemum almeriense, in order to evaluate their roles in tolerance to water deficit. Five cDNAs, named HaPIP1;1, HaPIP1;2, HaPIP2;1, HaPIP2;2, and HaTIP1;1, were isolated from H. almeriense. A phylogenetic analysis of deduced proteins confirmed that they belong to the water channel proteins family. The HaPIP1;1, HaPIP2;1, and HaTIP1;1 genes encode functional water channel proteins, as indicated by expression assays in Saccharomyces cere- visiae, showing divergent roles in the transport of water, CO2, and NH3. The expression patterns of the genes iso- lated from H. almeriense and of a previously described gene from Terfezia claveryi (TcAQP1) were analyzed in my- corrhizal and nonmycorrhizal plants cultivated under well- watered or drought-stress conditions. Some of the studied aquaporins were subjected to fine-tuned expression only under drought-stress conditions. A beneficial effect on plant physiological parameters was observed in mycorrhi- zal plants with respect to nonmycorrhizal ones. Moreover, stress induced a change in the mycorrhizal type formed, which was more intracellular under drought stress. The combination of a high intracellular colonization, together with the fine-tuned expression of aquaporins could result in a morphophysiological adaptation of this symbiosis to drought conditions.