The endophytic fungus Serendipita indica helps to reduce Na+ accumulation in plants exposed to salinity

It has been described that the endophytic fungus Serendipita indica (formerly called Piriformospora indica) improves the growth and development of plants when exposed to adverse conditions, such as saline environments. However, the mechanism by which Serendipita improves plant growth has not yet been elucidated. In this work we show that Serendipita reduces the Na⁺ content of Arabidopsis plants when it grows in saline conditions. We also show that a localized and transient alkalinization occurs during the first stages of infection of the plant, a signal that could constitute a response to the infection that regulates further processes. In addition, we describe for the first time the characterization and functional regulation of the two Serendipita ENA ATPases that function as Na⁺ efflux systems, and that are promising candidates to mediate salt tolerance induced by the fungus and participate in the response of Serendipita at high pH levels.