ERF transcription factors involved in salt response in tomato

ERF transcription factors are important regulatory components of ethylene signaling, known to be involved in plant development and stress responses by regulating the expression of ethylene responsive genes. However, relatively less is known about the function of ERF gene family in wild tomato response to salt stress. Previously, we have carried out a microarray analysis on the salt-responsive genes in salt tolerant wild tomato Solanum pimpinellifolium ‘PI365967’. Five ERF genes (SpERFs) with induced expression upon salt treatment were subsequently selected for further characterization. Sequence analysis revealed that the seven amino acid residues in ERF proteins which are critical for their binding to the GCC-box in the promoter of ethylene responsive genes were conserved in five SpERFs. Two of five SpERFs (SpERF.B7 and SpERF.C11) belong to B3 sub-group as predicted by phylogenetic analysis. Expression analysis indicated that two SpERFs of B3 sub-group were more strongly induced in salt-tolerant genotypes than in salt-sensitive genotypes, in the order of PI365967 > LA2711 > Moneymaker, suggesting a positive role of B3 sub-group SpERFs in salt stress in tomato. To further confirm the function of B3 SpERFs in salt response, SpERF.B7 (one of two B3 SpERFs) was over-expressed in Arabidopsis. Consistent with our expectation, transgenic lines exhibited enhanced salt tolerance. These results will provide useful information for improving salt tolerance in tomato breeding in the future.