Modulation of Aquaporin Genes by the Arbuscular Mycorrhizal Symbiosis in Relation to Osmotic Stress Tolerance

Abstract

This chapter summarizes the current information regarding alteration of aquaporin-encoding genes by the arbuscular mycorrhizal (AM) symbiosis, and the relation between the modulation of aquaporin genes and the enhanced tolerance to osmotic stresses conferred by the AM symbiosis. The results obtained so far show that the effects of the symbiosis on PIP gene expression depends on the intrinsic properties of the osmotic stress itself. Under drought stress conditions, the AM symbiosis usually decreases or anticipates the decrease of PIP gene expression. Under salt stress, the trend was just the opposite as the AM symbiosis enhanced the expression of most of the PIP genes analyzed. The regulation of PIP gene expression under cold stress is less evident as one of the genes analyzed was down-regulated by the AM symbiosis, another was up-regulated, and two genes were not affected by the symbiosis, under such conditions. It seems also that the effects of the AM symbiosis on PIP gene expression depends on the endogenous levels of ABA in the host plant. In any case, the induction or inhibition of particular aquaporins by AM symbiosis should result in a better regulation of plant water status and contribute to the global plant resistance to the stressful conditions as evidenced by their better growth and water status under conditions of water deficit. However, aquaporins could be also be involved in the symbiotic exchange processes between the AM fungus and the plant, which opens new perspectives in the study of aquaporins in the AM symbiosis.