Ethylene-Induced Stabilization of ETHYLENE INSENSITIVE3 and EIN3-LIKE1 Is Mediated by Proteasomal Degradation of EIN3 Binding F-Box 1 and 2 That Requires EIN2 in Arabidopsis    

Abstract

Plant responses to ethylene are mediated by regulation of EBF1/2-dependent degradation of the ETHYLENE INSENSITIVE3 (EIN3) transcription factor. Here, we report that the level of EIL1 protein is upregulated by ethylene through an EBF1/2-dependent pathway. Genetic analysis revealed that EIL1 and EIN3 cooperatively but differentially regulate a wide array of ethylene responses, with EIL1 mainly inhibiting leaf expansion and stem elongation in adult plants and EIN3 largely regulating a multitude of ethylene responses in seedlings. When EBF1 and EBF2 are disrupted, EIL1 and EIN3 constitutively accumulate in the nucleus and remain unresponsive to exogenous ethylene application. Further study revealed that the levels of EBF1 and EBF2 proteins are downregulated by ethylene and upregulated by silver ion and MG132, suggesting that ethylene stabilizes EIN3/EIL1 by promoting EBF1 and EBF2 proteasomal degradation. Also, we found that EIN2 is indispensable for mediating ethylene-induced EIN3/EIL1 accumulation and EBF1/2 degradation, whereas MKK9 is not required for ethylene signal transduction, contrary to a previous report. Together, our studies demonstrate that ethylene similarly regulates EIN3 and EIL1, the two master transcription factors coordinating myriad ethylene responses, and clarify that EIN2 but not MKK9 is required for ethylene-induced EIN3/EIL1 stabilization. Our results also reveal that EBF1 and EBF2 act as essential ethylene signal transducers that by themselves are subject to proteasomal degradation.

Activation of ethylene signaling is mediated by nuclear translocation of the cleaved EIN2 carboxyl terminus

“…Previous studies revealed that EIN2 is required for EIN3 and EIL1 protein accumulation [6,10]. We found that while EIN3 protein was undetectable in the ein2 mutant, expression of CEND in ein2 led to the re-accumulation of EIN3 protein (Supplementary information, Figure S3A).…”

“…EIN2 was reported to localize at the ER membrane when transiently expressed in tobacco leaf cells [4]. EIN3 (ETHYLENE INSENSITIVE3) and its homolog EIL1 (EIN3-LIKE1) are two nuclear-localized transcription factors genetically acting downstream of EIN2 [5,6]. However, it remains a long mystery on how the ethylene signal is transmitted from ER-located EIN2 into the nucleus to modulate EIN3/EIL1-directed transcription.…”

Differential Control of Ethylene Responses byGREEN-RIPEandGREEN-RIPE LIKE1Provides Evidence for Distinct Ethylene Signaling Modules in Tomato

“…Consequently, subfunctionalization is apparent at multiple steps of the ethylene signaling pathway. For example, EIN3 and EIL1 proteins act semiredundantly to influence separate ethylene responses associated with seedling growth and stem and leaf expansion in Arabidopsis, and individual ETH-YLENE RESPONSE FACTOR genes mediate distinct responses to environmental stress (Hattori et al, 2009;An et al, 2010;Zhang et al, 2011). Subfunctionalization also occurs at the level of the ethylene receptors, with specific or more prevalent roles for individual receptors and receptor subfamilies identified, even though, in general, the ethylene receptors act redundantly (Tieman et al, 2000;Binder et al, 2006Binder et al, , 2012Qu et al, 2007;Plett et al, 2009;Wuriyanghan et al, 2009).…”

ETHYLENE-INSENSITIVE3 Is a Senescence-Associated Gene That Accelerates Age-Dependent Leaf Senescence by Directly Repressing miR164 Transcription in Arabidopsis

“…In addition to EIN3, the Arabidopsis genome encodes five EIN3-Like (EIL) transcription factors (Chao et al, 1997), wherein EIN3 and EIL1, its closest homolog, seem to mediate the vast majority of ethyleneregulated processes (Alonso et al, 2003;Binder et al, 2004). Genetic and biochemical studies revealed that EIN3 and EIL1 functions overlap, and both are subject to proteasomal degradation mediated by the F-box proteins EIN3-BINDING F BOX PROTEIN1 (EBF1) and EBF2 in the absence of ethylene signal (Guo and Ecker, 2003;Potuschak et al, 2003;Gagne et al, 2004;Binder et al, 2007;An et al, 2010).…”