Overexpression of a tomato AP2/ERF transcription factor SlERF.B1 increases sensitivity to salt and drought stresses

Ethylene response factors (ERFs) are unique to plants and play crucial roles in their response to various biotic and abiotic stresses, but the physiological and molecular mechanisms accounting for the functions of many ERF genes in abiotic stress are not well characterized in tomato. Here, an ERF gene, SlERF.B1 was characterized, which belongs to the IX subfamily of ERFs. SlERF.B1 expression was induced by salt, mannitol, cold, heat and ACC treatments, but repressed by ABA, IAA and 1-MCP treatments. The SlERF.B1 protein was nuclear-localized in tobacco and had no transcription activity in yeast. SlERF.B1-overexpression transgenic tomato and Arabidopsis exhibited significantly high sensitivity to salt treatment compared to wild-type at the phenotypic and physio-logical levels. Similarly, SlERF.B1-overexpression tomato plants exhibited lower tolerance to mannitol and drought stresses. Transcriptional analysis showed that transcript levels of several stress-responsive genes in SlERF.B1-overexpression lines were significantly inhibited under salt and drought stresses. Additionally, SlERF. B1 could repress SlARF5 (Auxin response factor 5) and SlER24 (ethylene-responsive transcriptional coactivator/ Multiprotein bridging factor 1) expressions by binding to dehydration-responsive element (DRE) in the pro-moters. Overall, the current results suggest that SlERF.B1 functions as a negative regulator of osmotic resistance.