Shaping Ethylene Response: The Role of EIN3/EIL1 Transcription Factors

Abstract

EIN3/EIL1 transcription factors are the key regulators of ethylene signaling that sustain a variety of plant responses to ethylene. Since ethylene regulates multiple aspects of plant development and stress responses, its signaling outcome needs proper modulation depending on the spatiotemporal and environmental conditions. In this review, we summarize recent advances on the molecular mechanisms that underlie EIN3/EIL1-directed ethylene signaling in Arabidopsis. We focus on the role of EIN3/EIL1 in tuning transcriptional regulation of ethylene response in time and space. Besides, we consider the role of EIN3/EIL1-independent regulation of ethylene signaling.

Keywords: ETHYLENE-INSENSITIVE3; ETHYLENE-INSENSITIVE3-LIKE; cross-talk; epigenetic regulation; protein–protein interactions.

Figure 1

The key components of ethylene signaling pathway. Gray and white circles depict negative and positive regulators of ethylene signaling, correspondingly. Position frequency matrix for Arabidopsis EIN3 binding motif (Chang et al., 2013) was retrieved from CIS-BP database (Weirauch et al., 2014) and visualized using Tomtom tool (http://meme-suite.org/tools/tomtom; Gupta et al. 2007). The model is based on the findings reported previously (Chang, 2016; Hu et al., 2017). The explanations are in the text. EBS, EIN3 binding site.

Figure 2

Tissue specificity of EIL genes expression. Publicly available datasets on transcriptome profiling of different Arabidopsis tissues (light- and dark-grown seedlings (Rühl et al., 2012; Oh et al., 2014), aerial tissues (Sani et al., 2013), leaf (Wollmann et al., 2012), root (Li et al., 2013), root and shoot apical meristems (Kang et al., 2014; Nozue et al., 2015), carpel (Martínez-Fernández et al., 2014), receptacle (Niederhuth et al., 2013), inflorescence (Gan et al., 2011), pollen (Loraine et al., 2013) were used for visualization. The corresponding expression levels were retrieved from ThaleMine v1.10.4 (https://apps.araport.org/thalemine/; Krishnakumar et al., 2017). TPM, transcripts per million.

Figure 3

Nuclear events that promote ethylene response. (A) Without ethylene, EIN3 undergoes EBF1/2-driven degradation. (B) Upon ethylene treatment, EIN3 is stabilized. On one hand, EIN2 C-terminal domain interacts with ENAP1, which results in elevation of H3K14Ac and H3K23Ac levels, facilitated EIN3 binding to the target promoters and activation of gene expression. On the other hand, SRT1 and SRT2 histone deacetylases mediate ethylene-directed transcriptional repression by downregulating the levels of H3K9 acetylation. The models are based on the findings reported previously (Gagne et al., 2004; Li et al., 2015; Merchante et al., 2015; Zhang et al., 2016; Zhang et al., 2017; Zhang et al., 2018a). Gray and white solid circles depict negative and positive regulators of ethylene signaling, correspondingly. EIN3 is depicted in orange, H3K9Ac—in red, H3K14Ac and H3K23Ac—in blue. Dashed circles denote putative regulators (with a question mark inside) and putative regulations (with a question mark outside). HAT, histone acetyltransferase; 26S, 26S proteasome.