ETHYLENE REGULATES ARABIDOPSIS SEED DORMANCY VIA A CROSSTALK WITH GIBBERELLINS AND ABSCISIC ACID AND THE N-END RULE PATHWAY
Yesbergenova-Cuny, Z., Wang, X., Biniek, C., Bailly, C. and Corbineau, F.
Seed Biology, UMR 7622 CNRS-UPMC, Sorbonne Universités, Paris, France
Contact: Françoise Corbineau, firstname.lastname@example.org
Arabidopsis seed dormancy corresponds to an inability to germinate in darkness at temperature higher than 10°C, and its regulation by the hormonal balance between abscisic acid (ABA) and gibberellins (GAs) is well documented. Ethylene (10-100 ppm) also strongly stimulates the germination of dormant seeds placed at 25°C. All the mutants affected in the ethylene signalling pathway (etr1, ein2, ain1, ein4 and erf) are dormant since they do not germinate at 25°C, but easily germinate at 15°C, except etr1, which is more dormant, suggesting the involvement of ethylene in the regulation of dormancy. Three to 4 days of stratification at 4-5°C promote germination at 25°C of all mutants including the ethylene insensitive ones (etr1, ain1, ein2), suggesting that cold can act directly on germination by bypassing the ethylene signalling pathway although it induces an accumulation of ETR1, EIN4, EIN2 and AIN1 transcripts. Two mutants (ain1 and etr1) that do not respond to exogenous ethylene, do not also respond to GA3, but GA3 synergically acts with exogenous ethylene in ain1 mutant. Germination at 15°C is inhibited by ABA, etr1 being the highest sensitive, suggesting a crosstalk between ABA and ethylene. This inhibitory effect of ABA is reversible by exogenous ethylene. Stronger dormancy of etr1 and ain1 mutant seeds, and low responsiveness to ethylene of Cyp 707A1 mutant confirm a crosstalk between ABA and ethylene at the level of ABA catabolism. Seed responsiveness to ethylene is regulated by the N-end rule pathway of the proteolysis, since mutants affected in this pathway (PRT6, ATE1-ATE2) do not respond to this hormone. Using mutants affected in the ERF-VII (Rap2.2, Rap 2.3, Rap2.12, Hre1, and Hre2) potential substrate of the N-end rule pathway, the involvement of this pathway in the regulation of seed dormancy is discussed as related to ethylene signalling.