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Summary: Arabidopsis histone H3 lysine 4 (H3K4) demethylases play crucial roles in several developmental processes, but their involvement in seedling establishment remain unexplored.Here, we show that Arabidopsis JUMONJI DOMAIN‐CONTAINING PROTEIN17 (JMJ17), an H3K4me3 demethylase, is involved in cotyledon greening during seedling establishment. Dark‐grown seedlings of jmj17 accumulated a high concentration of protochlorophyllide, an intermediate metabolite in the tetrapyrrole biosynthesis (TPB) pathway that generates chlorophyll (Chl) during photomorphogenesis. Upon light irradiation, jmj17 mutants displayed decreased cotyledon greening and reduced Chl level compared with the wild‐type; overexpression of JMJ17 completely rescued the jmj17‐5 phenotype.Transcriptomics analysis uncovered that several genes encoding key enzymes involved in TPB were upregulated in etiolated jmj17 seedlings. Consistently, chromatin immunoprecipitation‐quantitative PCR revealed elevated H3K4me3 level at the promoters of target genes. Chromatin association of JMJ17 was diminished upon light exposure. Furthermore, JMJ17 interacted with PHYTOCHROME INTERACTING FACTOR1 in the yeast two‐hybrid assay.JMJ17 binds directly to gene promoters to demethylate H3K4me3 to suppress PROTOCHLOROPHYLLIDE OXIDOREDUCTASE C expression and TPB in the dark. Light results in de‐repression of gene expression to modulate seedling greening during de‐etiolation. Our study reveals a new role for histone demethylase JMJ17 in controlling cotyledon greening in etiolated seedlings during the dark‐to‐light transition. See also the Commentary on this article by Woodson, 231: 907–909. [ABSTRACT FROM AUTHOR]

Summary: ETHYLENE OVERPRODUCER1 (ETO1), ETO1‐LIKE1 (EOL1), and EOL2 are members of the Broad complex, Tramtrack, Bric‐a‐brac (BTB) protein family that collectively regulate type‐2 1‐aminocyclopropane‐1‐carboxylic acid synthase (ACS) activity in Arabidopsis thaliana. Although ETO1 and EOL1/EOL2 encode structurally related proteins, genetic studies suggest that they do not play an equivalent role in regulating ethylene biosynthesis. The mechanistic details underlying the genetic analysis remain elusive. In this study, we reveal that ETO1 collaborates with EOL1/2 to play a key role in the regulation of type‐2 ACS activity via protein–protein interactions. ETO1, EOL1, and EOL2 exhibit overlapping but distinct tissue‐specific expression patterns. Nevertheless, neither EOL1 nor EOL2 can fully complement the eto1 phenotype under control of the ETO1 promoter, which suggests differential functions of ETO1 and EOL1/EOL2. ETO1 forms homodimers with itself and heterodimers with EOLs. Furthermore, CULLIN3 (CUL3) interacts preferentially with ETO1. The BTB domain of ETO1 is sufficient for interaction with CUL3 and is required for homodimerization. However, domain‐swapping analysis in transgenic Arabidopsis suggests that the BTB domain of ETO1 is essential but not sufficient for a full spectrum of ETO1 function. The missense mutation in eto1‐5 generates a substitution of phenylalanine with an isoleucine in ETO1F466I that impairs its dimerization and interaction with EOLs but does not affect binding to CUL3 or ACS5. Overexpression of ETO1F466I in Arabidopsis results in a constitutive triple response phenotype in dark‐grown seedlings. Our findings reveal the mechanistic role of protein–protein interactions of ETO1 and EOL1/EOL2 that is crucial for their biological function in ethylene biosynthesis. Significance Statement: The ETO1 family proteins function collectively as negative regulators of ethylene biosynthesis by promoting protein degradation of type‐2 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthase via differential association with CULLIN3 (CUL3)‐RING E3 ubiquitin ligases (CRL3) in Arabidopsis thaliana. This study provides a mechanistic view of such a regulation, which is dependent on the ability of ETO1 to form homodimers and dimerize with EOL1 and EOL2 to incorporate type‐2 ACC synthase into the CRL3ETO1/EOL complex for protein ubiquitination followed by degradation via the 26S proteasome. [ABSTRACT FROM AUTHOR]

The plant hormone ethylene plays a regulatory role in development in light- and dark-grown seedlings. We previously isolated a group of small-molecule compounds with a quinazolinone backbone, which were named acsinones (for AC C s ynthase in hibitor quinazoli nones), that act as uncompetitive inhibitors of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS). Thus, the triple response phenotype, which consists of shortened hypocotyls and roots, radial swelling of hypocotyls and exaggerated curvature of apical hooks, was suppressed by acsinones in dark-grown (etiolated) ethylene overproducer (eto) seedlings. Here, we describe our isolation and characterization of an Arabidopsis r evert to et o1 9 (ret9) mutant, which showed reduced sensitivity to acsinones in etiolated eto1 seedlings. Map-based cloning of RET9 revealed an amino acid substitution in CHITINASE LIKE1 (CTL1), which is required for cell wall biogenesis and stress resistance in Arabidopsis. Etiolated seedlings of ctl1ret 9 showed short hypocotyls and roots, which were augmented in combination with eto1-4. Consistently, ctl1ret 9 seedlings showed enhanced sensitivity to exogenous ACC to suppress primary root elongation as compared with the wild type. After introducing ctl1ret 9 to mutants completely insensitive to ethylene, genetic analysis indicated that an intact ethylene response pathway is essential for the alterations in root and apical hook but not hypocotyl in etiolated ctl1ret 9 seedlings. Furthermore, a mild yet significantly increased ethylene level in ctl1 mutants was related to elevated mRNA level and activity of ACC oxidase (ACO). Moreover, genes associated with ethylene biosynthesis (ACO1 and ACO2) and response (ERF1 and EDF1) were upregulated in etiolated ctl1ret 9 seedlings. By characterizing a new recessive allele of CTL1 , we reveal that CTL1 negatively regulates ACO activity and the ethylene response, which thus contributes to understanding a role for ethylene in root elongation in response to perturbed cell wall integrity. [ABSTRACT FROM AUTHOR]

The ERF (ethylene responsive factor) family is composed of transcription factors ( TFs) that are critical for appropriate A rabidopsis thaliana responses to biotic and abiotic stresses. Here we identified and characterized a member of the ERF TF group IX, namely ERF96, that when overexpressed enhances A rabidopsis resistance to necrotrophic pathogens such as the fungus B otrytis cinerea and the bacterium P ectobacterium carotovorum. ERF96 is jasmonate ( JA) and ethylene ( ET) responsive and ERF96 transcripts accumulation was abolished in JA-insensitive coi1-16 and in ET-insensitive ein2-1 mutants. Protoplast transactivation and electrophoresis mobility shift analyses revealed that ERF96 is an activator of transcription that binds to GCC elements. In addition, ERF96 mainly localized to the nucleus. Microarray analysis coupled to chromatin immunoprecipitation- PCR of A rabidopsis overexpressing ERF96 revealed that ERF96 enhances the expression of the JA/ ET defence genes PDF1.2a, PR -3 and PR -4 as well as the TF ORA59 by direct binding to GCC elements present in their promoters. While ERF96- RNAi plants demonstrated wild-type resistance to necrotrophic pathogens, basal PDF1.2 expression levels were reduced in ERF96-silenced plants. This work revealed ERF96 as a key player of the ERF network that positively regulates the A rabidopsis resistance response to necrotrophic pathogens. [ABSTRACT FROM AUTHOR]

Aneuploidy features a numerical chromosome variant that the number of chromosomes in the nucleus of a cell is not an exact multiple of the haploid number, which may have an impact on morphology and gene expression. Here we report a tertiary trisomy uncovered by characterizing a T-DNA insertion mutant (aur2-1/+) in the Arabidopsis (Arabidopsis thaliana) AURORA2 locus. Whole-genome analysis with DNA tiling arrays revealed a chromosomal translocation linked to the aur2-1 allele, which collectively accounted for a tertiary trisomy 2. Morphologic, cytogenetic and genetic analyses of aur2-1 progeny showed impaired male and female gametogenesis to various degrees and a tight association of the aur2-1 allele with the tertiary trisomy that was preferentially inherited. Transcriptome analysis showed overlapping and distinct gene expression profiles between primary and tertiary trisomy 2 plants, particularly genes involved in response to stress and various types of external and internal stimuli. Additionally, transcriptome and gene ontology analyses revealed an overrepresentation of nuclear-encoded organelle-related genes functionally involved in plastids, mitochondria and peroxisomes that were differentially expressed in at least three if not all Arabidopsis trisomics. These observations support a previous hypothesis that aneuploid cells have higher energy requirement to overcome the detrimental effects of an unbalanced genome. Moreover, our findings extend the knowledge of the complex nature of the T-DNA insertion event influencing plant genomic integrity by creating high-grade trisomy. Finally, gene expression profiling results provide useful information for future research to compare primary and tertiary trisomics for the effects of aneuploidy on plant cell physiology. [ABSTRACT FROM AUTHOR]