Modulation of ethylene responses affects plant salt-stress responses.

Ethylene signaling plays important roles in multiple aspects of plant growth and development. Its functions in abiotic stress responses remain largely unknown. Here, we report that alteration of ethylene signaling affected plant salt-stress responses. A type II ethylene receptor homolog gene NTHK1 (Nicotiana tabacum histidine kinase 1) from tobacco (N. tabacum) conferred salt sensitivity in NTHK1-transgenic Arabidopsis (Arabidopsis thaliana) plants as judged from the phenotypic change, the relative electrolyte leakage, and the relative root growth under salt stress. Ethylene precursor 1-aminocyclopropane-1-carboxylic acid suppressed the salt-sensitive phenotype. Analysis of Arabidopsis ethylene receptor gain-of-function mutants further suggests that receptor function may lead to salt-sensitive responses. Mutation of EIN2, a central component in ethylene signaling, also results in salt sensitivity, suggesting that EIN2-mediated signaling is beneficial for plant salt tolerance. Overexpression of the NTHK1 gene or the receptor gain-of-function activated expression of salt-responsive genes AtERF4 and Cor6.6. In addition, the transgene NTHK1 mRNA was accumulated under salt stress, suggesting a posttranscriptional regulatory mechanism. These findings imply that ethylene signaling may be required for plant salt tolerance.