EIN3 Transcriptionally Regulates ESE1 Expression To Increase Salt Tolerance In Arabidopsis Thaliana

Ethylene is a very important gas hormone that participates in many aspects of plant growth, development, senescence, and responses to biotic and abiotic stresses. Accumulating evidence indicates that ethylene signaling pathway regulates salt stress. In such modulation, transcriptional control conferred by transcription factor EIN3 is pivotal, however, very little is known about the downstream targets of EIN3 in the ethylene signaling-dependent salt response. It is reported that some ERF proteins play crucial roles under salt stress, we propose whether EIN3 directly targets the expression of ERF genes.In this report, through mining a large amount of microarray data, we identified 31 ERF genes that might be involved in ethylene signaling pathway. 5 of these genes are induced by ACC (1-aminocyclopropane-1-carboxylic acid), ethylene and salt, but repressed by AgNO3 and AVG (aminoethoxyvinylglycine), respectively. At3g23220 was confirmed with real-time quantitative PCR, which was induced by ACC and salt, but repressed by AgNO3 and AVG, suggesting that At3g23220 might be involved in ethylene and salt response. Thus we named it ethylene and salt inducible ERF gene 1 as ESE1. Moreover, the expression of ESE1 was decreased in ein2, ein3-1 and eill-3 mutants but enhanced in plants overexpressing EIN3, evidencing that ESE1 was not only salt inducible but also transcriptionally monitored by ethylene-signaling component EIN3.Further analyses with biochemical and molecular approaches revealed that the N-terminal of EIN3 specifically binds to the P2-3 (-282—-246) region of the ESE1 promoter. More importantly, the knockdown mutant esel enhanced salt sensitivity while overexpression of ESE1 had high seed germination rate and showed salt-tolerant phenotype under salt stress, compared to Col-0. Additionally, overexpression of ESE1 in ein3-1 mutant can rescue salt-sensitive phenotype, indicating the essential downstream regulation of ESE1 in EIN3-dependent salt response. Further more, ESE1 is a novel ERF protein, which had transcriptional activation activity and can bind to DRE and GCC box in vivo and in vitro. The overexpression of EIN3 or ESE1 coincidently activated the expression of salt-related and DRE/GCC box-containing genes, elucidating a crucial event of the EIN3-ESE1 transcriptional complex activating the expression of salt-related genes in salt response.