Isolation, molecular characterization, and functional analysis of the vacuolar Na+/H+ antiporter genes from the halophyte Karelinia caspica

The full-length cDNAs of two Karelinia caspica genes, KcNHX1 and KcNHX2, were isolated by RACE and RT-PCR based on the conserved regions of Na+/H+ antiporter (NHX) genes from other halophyte species. The cloned KcNHX1 cDNA contained 2,022 nucleotides with an open reading frame (ORF) of 1,620 bp and the KcNHX2 cDNA contained 1,976 nucleotides with an ORF of 1,653 bp. The deduced amino acid sequences indicated that both genes were homologous to NHXs from other higher plants. To investigate the possible roles of KcNHX1 and KcNHX2 in the salt stress response of K. caspica and the underlying regulatory mechanisms, RNAi vectors were constructed and transformed into K. caspica to specifically silence endogenous KcNHX1 and KcNHX2. The physiological results showed that silencing KcNHX1 in K. caspica led to reduced salt tolerance in high concentrations of NaCl, suggesting that KcNHX1 plays an essential role in the response of K. caspica to salt stress. However, the inhibition of KcNHX2 seemed to have little influence on the salt resistance of transgenic plants, indicating that KcNHX2 may be relevant for functions other than salt tolerance in K. caspica.