Ethylene gas is essential for many developmental processes and stress responses in plants. EIN2 plays a key role in ethylene signalling but its function remains enigmatic. Here, we show that ethylene specifically elevates acetylation of histone H3K14 and the non-canonical acetylation of H3K23 in etiolated seedlings. The up-regulation of these two histone marks positively correlates with ethylene-regulated transcription activation, and the elevation requires EIN2. Both EIN2 and EIN3 interact with a SANT domain protein named EIN2 nuclear associated protein 1 (ENAP1), overexpression of which results in elevation of histone acetylation and enhanced ethylene-inducible gene expression in an EIN2-dependent manner. On the basis of these findings we propose a model where, in the presence of ethylene, the EIN2 C terminus contributes to downstream signalling via the elevation of acetylation at H3K14 and H3K23. ENAP1 may potentially mediate ethylene-induced histone acetylation via its interactions with EIN2 C terminus.

Ethylene gas is essential for developmental processes and stress responses in plants. Although the membrane-bound protein EIN2 is critical for ethylene signaling, the mechanism by which the ethylene signal is transduced remains largely unknown. Here we show the levels of H3K14Ac and H3K23Ac are correlated with the levels of EIN2 protein and demonstrate EIN2 C terminus (EIN2-C) is sufficient to rescue the levels of H3K14/23Ac of ein2-5 at the target loci, using CRISPR/dCas9-EIN2-C. Chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) and ChIP-reChIP-seq analyses revealed that EIN2-C associates with histone partially through an interaction with EIN2 nuclear-associated protein1 (ENAP1), which preferentially binds to the genome regions that are associated with actively expressed genes both with and without ethylene treatments. Specifically, in the presence of ethylene, ENAP1-binding regions are more accessible upon the interaction with EIN2, and more EIN3 proteins bind to the loci where ENAP1 is enriched for a quick response. Together, these results reveal EIN2-C is the key factor regulating H3K14Ac and H3K23Ac in response to ethylene and uncover a unique mechanism by which ENAP1 interacts with chromatin, potentially preserving the open chromatin regions in the absence of ethylene; in the presence of ethylene, EIN2 interacts with ENAP1, elevating the levels of H3K14Ac and H3K23Ac, promoting more EIN3 binding to the targets shared with ENAP1 and resulting in a rapid transcriptional regulation.T he plant hormone ethylene is essential for a myriad of physiological and developmental processes. It is important in responses to stress, such as drought, cold, flooding, and pathogen infection (1, 2), and modulates stem cell division (3). The common aquatic ancestor of plants possessed the ethylene signaling pathway and the mechanism has been elucidated by analysis of Arabidopsis (4). Ethylene is perceived by a family of receptors bound to the membrane of the endoplasmic reticulum (ER) that are similar in sequence and structure to bacterial two-component histidine kinases (5-9). Each ethylene receptor has an N-terminal transmembrane domain, and the receptors form dimers that bind ethylene via a copper cofactor RAN1 (10, 11). Signaling from one of the receptors, ETR1, induces its physical association with the ER-localized protein RTE1 (12). The ethylene receptors function redundantly to negatively regulate ethylene responses (5) via a downstream Raf-like protein kinase called CTR1 (13,14).In the absence of ethylene, both the ethylene receptors and CTR1 are active, and CTR1 is associated with the ER membrane through a direct interaction with ETR1 (13). The CTR1 downstream factor, EIN2, is localized to the ER membrane, where it interacts with ETR1 (15). The protein stability of EIN2 is regulated by two F-box proteins, ETP1 and ETP2, which mediated its degradation by the ubiquitin-proteasome pathway (16). In the absence of ethylene, the CTR1-mediated phosphorylation at the C-terminal end of EIN2 (EIN2-C) leads to ...

Summary Under dehydration in plants, antagonistic activities of histone 3 lysine 4 (H3K4) methyltransferase and histone demethylase maintain a dynamic and homeostatic state of gene expression by orientating transcriptional reprogramming toward growth or stress tolerance. However, the histone demethylase that specifically controls histone methylation homeostasis under dehydration stress remains unknown. Here, we document that a histone demethylase, JMJ17, belonging to the KDM5/JARID1 family, plays crucial roles in response to dehydration stress and abscisic acid (ABA) in Arabidopsis thaliana. jmj17 loss‐of‐function mutants displayed dehydration stress tolerance and ABA hypersensitivity in terms of stomatal closure. JMJ17 specifically demethylated H3K4me1/2/3 via conserved iron‐binding amino acids in vitro and in vivo. Moreover, H3K4 demethylase activity of JMJ17 was required for dehydration stress response. Systematic combination of genome‐wide chromatin immunoprecipitation coupled with massively parallel DNA sequencing (ChIP‐seq) and RNA‐sequencing (RNA‐seq) analyses revealed that a loss‐of‐function mutation in JMJ17 caused an ectopic increase in genome‐wide H3K4me3 levels and activated a plethora of dehydration stress‐responsive genes. Importantly, JMJ17 bound directly to the chromatin of OPEN STOMATA 1 (OST1) and demethylated H3K4me3 for the regulation of OST1 mRNA abundance, thereby modulating the dehydration stress response. Our results demonstrate a new function of a histone demethylase under dehydration stress in plants.

Ethylene is an important phytohormone with pleotropic roles in plant growth, development, and stress responses. ETHYLENE INSENSITIVE2 (EIN2) mediates the transduction of the ethylene signal from the endoplasmic reticulum membrane to the nucleus, where its C-terminus (EIN2-C) regulates histone acetylation to mediate transcriptional regulation by EIN3. However, no direct interaction between EIN2-C and EIN3 has been detected. To determine how EIN2-C and EIN3 act together, we followed a synthetic approach and engineered a chimeric EIN2-C with EIN3 DNA-binding activity but lacking its transactivation activity (EIN2C–EIN3DB). The overexpression of EIN2C–EIN3DB in either wild-type or in the ethylene-insensitive mutant ein3-1 eil1-1 led to a partial constitutive ethylene response. Chromatin immunoprecipitation sequencing showed that EIN2C–EIN3DB has DNA-binding activity, indicating that EIN3DB is functional in EIN2C–EIN3DB. Furthermore, native EIN3 protein levels determine EIN2C–EIN3DB binding activity and binding targets in a positive feedback loop by interacting with EIN2C–EIN3DB to form a heterodimer. Additionally, although EIN3 does not direct affect histone acetylation levels in the absence of EIN2, it is required for the ethylene-induced elevation of H3K14Ac and H3K23Ac in the presence of EIN2. Together, we reveal efficient and specific DNA-binding by dimerized EIN3 in the presence of ethylene to mediate positive feedback regulation, which is required for EIN2-directed elevation of histone acetylation to integrate into an EIN3-dependent transcriptional activation.

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