Revisiting the Role of Ethylene and N-End Rule Pathway on Chilling-Induced Dormancy Release in Arabidopsis Seeds.

Dormant Arabidopsis () seeds do not germinate easily at temperatures higher than 10⁻15 °C. Using mutants affected in ethylene signaling (, and ) and in the N-end-rule pathway of the proteolysis ( and ) we have investigated the effects of cold and ethylene on dormancy alleviation. Ethylene (10⁻100 ppm) and 2⁻4 days chilling (4 °C) strongly stimulate the germination of wild type (Col-0) seeds at 25 °C. Two to four days of chilling promote the germination at 25 °C of all the mutants suggesting that release of dormancy by cold did not require ethylene and did not require the N-end-rule pathway. One mutant () that did not respond to ethylene did not respond to GA₃ either. Mutants affected in the N-end rule ( and ) did not respond to ethylene indicating that also this pathway is required for dormancy alleviation by ethylene; they germinated after chilling and in the presence of GA₃. Cold can activate the ethylene signaling pathway since it induced an accumulation of , EINI4, and transcripts, the expression of which was not affected by ethylene and GA₃. Both cold followed by 10 h at 25 °C and ethylene downregulated the expression of , ATE1, ATE2, and of involved in ABA signaling as compared to dormant seeds incubated at 25 °C. In opposite, the expression of , GAI, and encoding three DELLAs was induced at 4 °C but downregulated in the presence of ethylene.