Survive or die? A molecular insight into salt-dependant signaling network

• The complex molecular and physiological mechanisms of NaCl tolerance in Antirrhinum majus L. were dissected using a two-mode model, survival versus death and a multi-step experiment.
• Tolerance to the osmotic phase was associated to a better integration and transduction of NaCl stress into growth programs.
• The transcriptional reprogramming of Ca2+ signaling components were pivotal to modulate differential abilities to tolerate the salt.
• ABA and ethylene signaling pathway act as a positive regulators of salt acclimation.

The response of plants to salt stress involves dynamic changes in growth and signaling leading to successful adaptation or death. To elucidate how these opposed events are coordinated we identified a salt-tolerant (obesifruticosa) and a salt-sensitive (aestiva) Antirrhinum majus mutants using shoots as sensitive indicator of stress magnitude. A series of physiological tests were performed that compared the response after 6 h and 3 days of these contrasting mutants grown in agar under a single (200 mM) NaCl concentration, including shoot area, root length, relative water content, plant height, and overall biomass accumulation. Additional measurements of ABA content, chlorophyll degradation, ethylene production, net photosynthesis rates and Na+, K+, Ca2+, and Mg2+ content were also reported. RNA-seq analysis was performed on the two mutants after 6 h and 3 days under 200 mM NaCl. A total of 9199 transcripts were found to be differentially expressed in response to NaCl treatment in the two mutants. A large collection of known genes, including MAPKs, CDKs, CDPKs, CIPKs, various transcription factors, various ion transport proteins, and various genes involved in ABA and ethylene signaling pathways were described in detail that displayed differential expression profiles. Overall these data provided evidences of a putative osmotic tolerance sensing and signaling mechanism through a better integration and transduction of environmental cues into growth programs. The reprogramming of calcium-signaling components, generates specific stress signatures affecting differentially the salinity tolerance traits, such as tissue tolerance and anion exclusion. Interestingly, the hormones ABA and ethylene may action as a positive regulators of salt acclimation by the modulation of their signal transduction pathway.