Analysis of gene expression profiles in Arabidopsis salt overly sensitive mutants sos2-1 and sos3-1

Under salt-stress conditions, Arabidopsis salt overly sensitive (sos) mutants show hypersensitive root growth. The sos gene products are involved in ion transport and signalling processes. To analyse salt-stress-responsive genes whose transcripts are regulated by the SOS signalling pathway, we used a 22K Agilent oligoarray and quantitative real-time polymerase chain reaction analyses. The amounts of transcripts of the major salt-inducible genes (RD29A/COR78, RD17/COR47, COR15A, KIN1, and RD22) in sos mutants were similar to those in the wild-type plants. These results indicate that the SOS3/SOS2 signalling pathway is independent of the DRE/CRT, ABRE, and MYC/MYB pathways. In sos2 mutants, the expression levels of 27 and 48 genes were up-regulated at least double under 2-h and 5-h salt stress conditions, respectively. Among the genes regulated by SOS2, we detected several encoding myb family transcription factors, AP2 transcription factors, and some ethylene-related, auxin-induced, and defence-related genes. On the other hand, expression levels of very few genes were different between sos3 mutant and wild-type plants. This observation indicates that the downstream SOS2 affects the regulation of stress-responsive genes much more strongly than the upstream SOS3. The gene expression profiles of sos2 and sos3 mutants were not identical. This indicates that SOS2 and SOS3 have individual roles in salt stress responses in addition to common roles.