Expression levels and promoter activities of candidate salt tolerance genes in halophytic and glycophytic Brassicaceae

Expression of NHX1 genomic DNA under the C. x hollandica NHX1 promoter in the A.t.nhx1 mutant background yielded, irrespective of the genomic DNA source, 20-fold and 2-fold enhanced expression levels, in comparison with those in wild-type A. thaliana and C. x hollandica, respectively. This suggests that the high expression level in C. x hollandica is completely explained by altered cis-regulation of this gene. Promoter swap experiments showed that the C. x hollandica SOS1 and VATD promoters were five-fold and two-fold more active than the corresponding A. thaliana promoters, respectively. However, particularly in the case of VATD, this is not sufficient to explain the difference in the wild-type expression levels between C. x hollandica and A. thaliana.