Arbuscular mycorrhizal symbiosis and salicylic acid regulate aquaporins and root hydraulic properties in maize plants subjected to drought

Climate change is leading to the intensification of drought effects worldwide, which considerably reduce crop production. A better understanding of the drought-tolerance mechanisms would lead into a more productive agriculture. The arbuscular mycorrhizal (AM) symbiosis has been shown to improve plant tolerance to drought. Salicylic acid (SA) is a phenolic compound involved in many aspects of plant growth and development. Apart from its role in biotic interactions, it is also involved in the regulation of important plant physiological processes, including plant water relations under stressful conditions. However, despite the importance of SA in plant physiology and in AM colonization, little is known about its effect on regulation of root water transport. Thus, the aim of this work was to study the combined effect of AM symbiosis and SA on root hydraulic properties under drought stress, with special focus on how these factors can alter radial root water transport pathways through aquaporin regulation. Also, the crosstalk between SA and other phytohormones was taken into account. Results showed that the AM symbiosis modifies root hydraulic responses to drought episodes. Under these conditions, AM plants showed increased Lpr and Lo. Exogenous SA application decreased Lpr and Lo under drought. SA modulation of water conductivity could be due to a fine-regulation of root aquaporins (as ZmPIP2;4 or ZmTIP1;1). Furthermore, SA application differently modulated the percentage of water flowing by the apoplastic pathway, decreasing its contribution to total root water flow in AM plants and increasing it in non-AM plants. An intricate relationship between Lpr, aquaporins and endogenous levels of SA, ABA and jasmonic acid was observed. Future studies should explore more in detail the crosstalk mechanism between these hormones in the regulation of water transport in AM roots, in order to better understand the mechanism through which the AM symbiosis copes with drought stress.