The Salt Overly Sensitive (SOS) signaling pathway that in Arabidopsis comprises the sodium transport protein SOS1, the protein kinase SOS2, and the calcium-dependent interacting proteins SOS3 and CBL10, has been shown to play a critical role in cellular signaling under salt stress. The SOS pathway maintains cellular ion homeostasis by mediating sodium extrusion at the root and the long distance transport of sodium ions from roots to shoots, thereby imparting salt tolerance to all plant species that have been genetically tested. Environmental challenges, including salinity, typically entail retardation of vegetative growth and delay or cessation of flowering. The flowering time regulator GIGANTEA (GI) is a key component in the photoperiodic control pathway of flowering. In Arabidopsis, GI is predominantly associated with the promotion of flowering in long-day growth. Recently, a molecular link has been discovered between GI and adaptation to salt stress that is mechanistically based on GI degradation under saline conditions, thereby retarding flowering (Kim et al., 2013). GI and the salt tolerance-related protein kinase SOS2 interact physically. In the absence of stress, the GI:SOS2 complex prevents SOS2-based activation of SOS1, the major plant Na/H antiporter mediating adaptation to salinity. GI-overexpressing, rapidly flowering plants show greater salt sensitivity, whereas gi mutants exhibit delayed flowering and enhanced salt tolerance, in correspondence with the physical status of SOS2. Salt-induced degradation of GI confers salt tolerance by the release of the SOS2 kinase. The GI¿SOS2 interaction introduces a higher order regulatory circuit that can explain in molecular terms, the long observed connection between floral transition and adaptive environmental stress tolerance in Arabidopsis.

This research was supported by grant BIO2012-36533 financed by the Spanish Ministry of Science and Innovation and the FEDER programme, and by the Next-Generation BioGreen 21 Programme (Systems and Synthetic Agrobiotech Centre, no. PJ008025), a Cooperative Research Programme for Agriculture Science and Technology Development (Project No. PJ007850) from the Rural Development Administration, and the Ministry of Education, Science and Technology for the World Class University (WCU) programme (R32-10148), Republic of Korea.

Comunicación oral presentada en el Congreso hispano-luso de Fisiología Vegetal FV2015 junto con la XIV reunión bienal conjunta de las Sociedades de Fisiología Vegetal de España y Portuga junio (del 14 al 17) Toledo

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