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Plants exhibit remarkable regeneration capacity, ensuring developmental plasticity. In vitro tissue culture techniques are based on plant regeneration ability and facilitate production of new organs and even the whole plant from explants. Plant somatic cells can be reprogrammed to form a pluripotent cell mass called the callus. A portion of pluripotent callus cells gives rise to a fertile shoot via de novo shoot organogenesis (DNSO). Here, we reconstitute the shoot regeneration process with four phases, namely pluripotency acquisition, shoot promeristem formation, establishment of the confined shoot progenitor, and shoot outgrowth. Additionally, other biological processes, including cell cycle progression and reactive oxygen species metabolism, which further contribute to successful completion of DNSO, are also summarized. Overall, this study highlights recent advances in the molecular and cellular events involved in DNSO, as well as the regulatory mechanisms behind key steps of DNSO., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The Evening Complex (EC) is a core component of the Arabidopsis ( Arabidopsis thaliana ) circadian clock, which represses target gene expression at the end of the day and integrates temperature information to coordinate environmental and endogenous signals. Here we show that the EC induces repressive chromatin structure to regulate the evening transcriptome. The EC component ELF3 directly interacts with a protein from the SWI2/SNF2-RELATED (SWR1) complex to control deposition of H2A.Z-nucleosomes at the EC target genes. SWR1 components display circadian oscillation in gene expression with a peak at dusk. In turn, SWR1 is required for the circadian clockwork, as defects in SWR1 activity alter morning-expressed genes. The EC-SWR1 complex binds to the loci of the core clock genes PSEUDO - RESPONSE REGULATOR7 ( PRR7 ) and PRR9 and catalyzes deposition of nucleosomes containing the histone variant H2A.Z coincident with the repression of these genes at dusk. This provides a mechanism by which the circadian clock temporally establishes repressive chromatin domains to shape oscillatory gene expression around dusk., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

Triacylglycerols (TAGs), a major lipid form of energy storage, are involved in a variety of plant developmental processes. While carbon reserves mainly accumulate in seeds, significant amounts of TAG have also been observed in vegetative tissues. Notably, the accumulation of leaf TAGs is influenced by environmental stresses such as drought stress, although underlying molecular networks remain to be fully elucidated. In this study, we demonstrate that the R2R3-type MYB96 transcription factor promotes TAG biosynthesis in Arabidopsis thaliana seedlings. Core TAG biosynthetic genes were up-regulated in myb96-ox seedlings, but down-regulated in myb96- deficient seedlings. In particular, ABA stimulates TAG accumulation in the vegetative tissues, and MYB96 plays a fundamental role in this process. Considering that TAG accumulation contributes to plant tolerance to drought stress, MYB96-dependent TAG biosynthesis not only triggers plant adaptive responses but also optimizes energy metabolism to ensure plant fitness under unfavorable environmental conditions.

The INDETERMINATE DOMAIN (IDD) genes comprise a conserved transcription factor family that regulates a variety of developmental and physiological processes in plants. Many recent studies have focused on the genetic characterization of IDD family members and revealed various biological functions, including modulation of sugar metabolism and floral transition, cold stress response, seed development, plant architecture, regulation of hormone signaling, and ammonium metabolism. In this review, we summarize the functions and working mechanisms of the IDD gene family in the regulatory network of metabolism and developmental processes.

Circadian clocks are conserved time-keeper mechanisms in some prokaryotes and higher eukaryotes. Chromatin modification is emerging as key regulatory mechanism for refining core clock gene expression. Rhythmic changes in histone marks are closely associated to the TIMING OF CAB EXPRESSION 1 ( TOC1 ) Arabidopsis clock gene. However, the chromatin-related modifiers responsible for these marks remain largely unknown. Here, we uncover that the chromatin modifier HISTONE DEACETYLASE 9 (HDA9) and the Evening complex (EC) component EARLY FLOWERING 3 (ELF3) directly interact to regulate the declining phase of TOC1 after its peak expression. We found that HDA9 specifically binds to the TOC1 promoter through the interaction with ELF3. The EC-HDA9 complex promotes H3 deacetylation at the TOC1 locus, contributing to suppressing TOC1 expression during the night, the time of EC function. Therefore, we have identified the mechanism by which the circadian clock intertwines with chromatin-related components to shape the circadian waveforms of gene expression in Arabidopsis ., Competing Interests: The authors declare no competing interests.

Unlike activation of target genes in response to abscisic acid (ABA), how MYB96 transcription factor represses ABA-repressible genes to further enhance ABA responses remains unknown. Here, we show MYB96 interacts with the histone modifier HDA15 to suppress negative regulators of early ABA signaling. The MYB96-HDA15 complex co-binds to the promoters of a subset of RHO GTPASE OF PLANTS (ROP) genes, ROP6, ROP10, and ROP11, and represses their expression by removing acetyl groups of histone H3 and H4 from the cognate regions, particularly in the presence of ABA. In support, HDA15-deficient mutants display reduced ABA sensitivity and are susceptible to drought stress with derepression of the ROP genes, as observed in the myb96-1 mutant. Biochemical and genetic analyses show that MYB96 and HDA15 are interdependent in the regulation of ROP suppression. Thus, MYB96 confers maximal ABA sensitivity by regulating both positive and negative regulators of ABA signaling through distinctive molecular mechanisms.

Plant cells have a remarkable plasticity that allows cellular reprogramming from differentiated cells and subsequent tissue regeneration. Callus formation occurs from pericycle-like cells through a lateral root developmental pathway, and even aerial parts can also undergo the cell fate transition. Pluripotent calli are then subjected primarily to shoot regeneration in in vitro tissue culture. Successful completion of plant regeneration from aerial explants thus entails a two-step conversion of tissue identity. Here we show that a single chromatin modifier, ARABIDOPSIS TRITHORAX 4 (ATX4)/SET DOMAIN GROUP 16, is dynamically regulated during plant regeneration to address proper callus formation and shoot regeneration. The ATX4 protein massively activates shoot identity genes by conferring H3K4me3 deposition at the loci. ATX4-deficient mutants display strong silencing of shoot identity and thus enhanced callus formation. Subsequently, de novo shoot organogenesis from calli is impaired in atx4 mutants. These results indicate that a series of epigenetic reprogramming of tissue identity underlies plant regeneration, and molecular components defining tissue identity can be used as invaluable genetic sources for improving crop transformation efficiency., (� The Author(s) 2019. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The circadian clock synchronizes endogenous rhythmic processes with environmental cycles and maximizes plant fitness. Multiple regulatory layers shape circadian oscillation, and chromatin modification is emerging as an important scheme for precise circadian waveforms. Here, we report the role of an evolutionarily conserved Sin3-histone deacetylase complex (HDAC) in circadian oscillation in Arabidopsis . SAP30 FUNCTION-RELATED 1 ( AFR1 ) and AFR2 , which are key components of Sin3-HDAC complex, are circadianly-regulated and possibly facilitate the temporal formation of the Arabidopsis Sin3-HDAC complex at dusk. The evening-expressed AFR proteins bind directly to the CIRCADIAN CLOCK ASSOCIATED 1 ( CCA1 ) and PSEUDO-RESPONSE REGULATOR 9 ( PRR9 ) promoters and catalyze histone 3 (H3) deacetylation at the cognate regions to repress expression, allowing the declining phase of their expression at dusk. In support, the CCA1 and PRR9 genes were de-repressed around dusk in the afr1-1afr2-1 double mutant. These findings indicate that periodic histone deacetylation at the morning genes by the Sin3-HDAC complex contributes to robust circadian maintenance in higher plants.

Plant regeneration involves critical checkpoints including pluripotency acquisition and de novo organogenesis. However, comprehensive understanding of the mechanisms that underlie plant regeneration remains limited. Here, we found that calli derived from jasmonate (JA)-pretreated hypocotyl explants exhibited increased rates of de novo shoot regeneration. In contrast, exogenous JA treatment during callus formation on CIM did not influence the plant regeneration process. The enhanced shoot regeneration was diminished in coi1-1 mutants, indicating that JA-pretreated explants potentiate shoot regeneration in a COI1-dependent manner. These results suggest that the JA-responsive COI1 protein likely contributes to plant regeneration efficiency via regulation of hormone-signaling crosstalk and/or cell proliferation.

Seeds contain a large quantity of oils, which are mainly constituted of triacylglycerol (TAG), a fundamental source of carbon and energy. TAG biosynthesis is catalyzed by a series of multiple enzymes. In particular, two key enzymes catalyzing the last acylation step for TAG production, acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) and phospholipid:diacylglycerol acyltransferase 1 (PDAT1), are rate-limiting enzymes that determine TAG accumulation in Arabidopsis seeds. We recently showed that the two enzymes are transcriptionally coordinated by the R2R3-type MYB96 transcription factor to promote TAG assembly during seed maturation in Arabidopsis. Here, we further found that DGAT1 and PDAT1 physically associate, possibly to enhance the efficiency of TAG production. Overall, our findings suggest that TAG biosynthesis is intricately regulated at multiple levels, and these molecular strategies can potentially be used for metabolic engineering in plants.

Temporal and spatial compartmentalization of biological processes is facilitated by tissue-specific uncoupled circadian clocks in plants. However, interactions among tissue-specific circadian clocks have not been well established. The primary objective of this study was to describe both organ-specific circadian behaviors and centralized actions of the root clock. We analyzed transcript accumulation of circadianly-oscillating genes in roots and shoots. Expression of many clock components was different in roots and shoots. In particular, evening-expressed clock components were highly expressed in roots and likely play important roles in oscillation of the root clock. Consistent with this, the root and shoot clocks responded differentially to circadian gene mutations. The root clock was even dampened in gi-2 mutant. Circadian clocks basically oscillate in an organ-specific manner in plants, but the root clock also requires shoot-derived signals for organism-level coordination of circadian activity.

Plant somatic cells can be reprogrammed by in vitro tissue culture methods, and massive genome-wide chromatin remodeling occurs, particularly during callus formation. Since callus tissue resembles root primordium, conversion of tissue identity is essentially required when leaf explants are used. Consistent with the fact that the differentiation state is defined by chromatin structure, which permits limited gene profiles, epigenetic changes underlie cellular reprogramming for changes to tissue identity. Although a histone methylation process suppressing leaf identity during leaf-to-callus transition has been demonstrated, the epigenetic factor involved in activation of root identity remains elusive. Here, we report that JUMONJI C DOMAIN-CONTAINING PROTEIN 30 (JMJ30) stimulates callus formation by promoting expression of a subset of LATERAL ORGAN BOUNDARIES-DOMAIN (LBD) genes that establish root primordia. The JMJ30 protein binds to promoters of the LBD16 and LBD29 genes along with AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 and activates LBD expression. Consistently, the JMJ30-deficient mutant displays reduced callus formation with low LBD transcript levels. The ARF-JMJ30 complex catalyzes the removal of methyl groups from H3K9me3, especially at the LBD16 and LBD29 loci to activate their expression during leaf-to-callus transition. Moreover, the ARF-JMJ30 complex further recruits ARABIDOPSIS TRITHORAX-RELATED 2 (ATXR2), which promotes deposition of H3K36me3 at the LBD16 and LBD29 promoters, and the tripartite complex ensures stable LBD activation during callus formation. These results indicate that the coordinated epigenetic modifications promote callus formation by establishing root primordium identity., (© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.)

Main Conclusion: The histone acetyltransferase HAF2 facilitates H3 acetylation deposition at the PRR5 and LUX promoters to contribute to robust circadian oscillation. The circadian clock ensures synchronization of endogenous rhythmic processes with environmental cycles. Multi-layered regulation underlies precise circadian oscillation, and epigenetic regulation is emerging as a crucial scheme for robust circadian maintenance. Here, we report that HISTONE ACETYLTRANSFERASE OF THE TAFII250 FAMILY 2 (HAF2) is involved in circadian homeostasis. The HAF2 gene is activated at midday, and its temporal expression is shaped by CIRCADIAN CLOCK-ASSOCIATED 1. The midday-activated HAF2 protein stimulates H3 acetylation (H3ac) deposition at the PRR5 and LUX loci, contributing to establishment of the raising phase. These results indicate that epigenetic waves in circadian networks underlie temporal compartmentalization of circadian components and stable maintenance of circadian oscillation.

Maturing seeds stimulate fatty acid (FA) biosynthesis and triacylglycerol (TAG) accumulation to ensure carbon and energy reserves. Transcriptional reprogramming is a key regulatory scheme in seed oil accumulation. In particular, TAG assembly is mainly controlled by the transcriptional regulation of two key enzymes, acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) and phospholipid:diacylglycerol acyltransferase 1 (PDAT1), in Arabidopsis seeds. However, the transcriptional regulators of these enzymes are as yet unknown. Here, we report that the R2R3-type MYB96 transcription factor regulates seed oil accumulation by activating the genes encoding DGAT1 and PDAT1, the rate-limiting enzymes of the last step of TAG assembly. Total FA levels are significantly elevated in MYB96-overexpressing transgenic seeds, but reduced in MYB96-deficient mutant seeds. Notably, MYB96 regulation of TAG accumulation is independent of WRINKLED 1 (WRI1)-mediated FA biosynthesis. Taken together, our findings indicate that FA biosynthesis and TAG accumulation are under independent transcriptional control, and MYB96 is mainly responsible for TAG assembly in seeds.

The circadian clock and cell cycle as separate pathways have been well documented in plants. Elucidating whether these two oscillators are connected is critical for understanding plant growth. We found that a slow-running circadian clock decelerates the cell cycle and, conversely, a fast clock speeds it up. The clock component TOC1 safeguards the G 1 -to-S transition and controls the timing of the mitotic cycle at early stages of leaf development. TOC1 also regulates somatic ploidy at later stages of leaf development and in hypocotyl cells. The S-phase is shorter and delayed in TOC1 overexpressing plants, which correlates with the diurnal repression of the DNA replication licensing gene CDC6 through binding of TOC1 to the CDC6 promoter. The slow cell-cycle pace in TOC1-ox also results in delayed tumor progression in inflorescence stalks. Thus, TOC1 sets the time of the DNA pre-replicative machinery to control plant growth in resonance with the environment., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Small peptides mediate cell-cell communication to coordinate a variety of plant developmental processes. Signaling peptides specifically bind to the extracellular domains of receptors that belong to the receptor-like kinase family, and the peptide-receptor interaction activates a range of biochemical and physiological processes. The plant root is crucial for the anchorage of plants in soil as well as for the uptake of water and nutrients. Over recent years great progress has been made in the identification of receptors, structural analysis of peptide-receptor pairs, and characterization of their signaling pathways during plant root development. We review here recent advances in the elucidation of the functions and molecular mechanisms of signaling peptides, the peptide-receptor pairs that activate signal initiation, and their signaling pathways during root development., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Tissue identity is plastically regulated in plants, and chromatin modifiers/remodelers are main players of cell fate changes. Callus formation is an intriguing example of cell fate transition. Leaf explants can form callus tissues, which resemble lateral root primordium, on callus-inducing medium (CIM). We recently demonstrated that the ARABIDOPSIS TRITHORAX-RELATED 2 (ATXR2) protein, which deposits H3K36me3 at genomic level, regulates callus formation on CIM. Consistent with the role of ATXR2 in conferring root identity, lateral root formation was significantly reduced in atxr2-deficient mutants. Furthermore, atxr2 mutants also displayed defects in adventitious root formation from wounded leaf tissues on hormone-free medium. Our findings indicate that ATXR2 is a genuine regulator of de novo root organogenesis.

Plants have the remarkable ability to drive cellular dedifferentiation and regeneration. Changes in epigenetic landscapes accompany the cell fate transition. Notably, modifications of chromatin structure occur primarily during callus formation via an in vitro tissue culture process and, thus, pluripotent callus cells have unique epigenetic signatures. Here, we highlight the latest progress in epigenetic regulation of callus formation in plants, which addresses fundamental questions related to cell fate changes and pluripotency establishment. Global and local modifications of chromatin structure underlie callus formation, and the combination and sequence of epigenetic modifications further shape intricate cell fate changes. This review illustrates how a series of chromatin marks change dynamically during callus formation and their biological relevance in plant regeneration., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Cellular dedifferentiation, the transition of differentiated somatic cells to pluripotent stem cells, ensures developmental plasticity and contributes to wound healing in plants. Wounding induces cells to form a mass of unorganized pluripotent cells called callus at the wound site. Explanted cells can also form callus tissues in vitro. Reversible cellular differentiation-dedifferentiation processes in higher eukaryotes are controlled mainly by chromatin modifications. We demonstrate that ARABIDOPSIS TRITHORAX-RELATED 2 (ATXR2), a histone lysine methyltransferase that promotes the accumulation of histone H3 proteins that are trimethylated on lysine 36 (H3K36me3) during callus formation, promotes early stages of cellular dedifferentiation through activation of LATERAL ORGAN BOUNDARIES DOMAIN ( LBD ) genes. The LBD genes of Arabidopsis thaliana are activated during cellular dedifferentiation to enhance the formation of callus. Leaf explants from Arabidopsis atxr2 mutants exhibited a reduced ability to form callus and a substantial reduction in LBD gene expression. ATXR2 bound to the promoters of LBD genes and was required for the deposition of H3K36me3 at these promoters. ATXR2 was recruited to LBD promoters by the transcription factors AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19. Leaf explants from arf7-1arf19-2 double mutants were defective in callus formation and showed reduced H3K36me3 accumulation at LBD promoters. Genetic analysis provided further support that ARF7 and ARF19 were required for the ability of ATXR2 to promote the expression of LBD genes. These observations indicate that the ATXR2-ARF-LBD axis is key for the epigenetic regulation of callus formation in Arabidopsis ., (Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Main Conclusion: The auxin-brassinosteroid interaction involving the BIN2-ARF-LBD axis plays a key role in temperature-dependent callus formation in Arabidopsis. An extensive web of multiple hormone signaling pathways underlies callus formation. Here, we report that a brassinosteroid (BR) signaling component, BR-INSENSITIVE 2 (BIN2), positively regulates callus formation. The BIN2 kinase promotes transcriptional activities of AUXIN RESPONSE FACTOR 7 (ARF7) and ARF19 and subsequently activates expression of LATERAL ORGAN BOUNDARIES-DOMAIN 16 (LBD16) and LBD29 during callus formation. Consistently, the BIN2 activity is dependent on ARFs in the control of callus formation. Notably, this auxin-BR interaction is particularly relevant in temperature-dependent callus formation. Misexpression of BIN2 and ARFs resulted in the temperature insensitivity of callus formation. These results indicate that the BIN2-ARF-LBD axis plays a key role in temperature-dependent callus formation in Arabidopsis.

Hypocotyl elongation is extensively controlled by hormone signaling networks. In particular, auxin metabolism and signaling play key roles in light-dependent hypocotyl growth. The nuclear matrix facilitates organization of DNA within the nucleus, and dynamic interactions between nuclear matrix and DNA are related to gene regulation. Conserved scaffold/matrix attachment regions (S/MARs) are anchored to the nuclear matrix by the AT-HOOK MOTIF CONTAINING NUCLEAR LOCALIZED (AHL) proteins in Arabidopsis. Here, we found that ESCAROLA (ESC)/AHL27 and SUPPRESSOR OF PHYTOCHROME B-4 #3 (SOB3)/AHL29 redundantly regulate auxin biosynthesis in the control of hypocotyl elongation. The light-inducible AHL proteins bind directly to an S/MAR region of the YUCCA 9 (YUC9) promoter and suppress its expression to inhibit hypocotyl growth in light-grown seedlings. In addition, they recruit the SWI2/SNF2-RELATED 1 (SWR1) complex and promote exchange of H2A with the histone variant H2A.Z at the YUC9 locus to further elaborately control auxin biosynthesis. Consistent with these results, the long hypocotyl phenotypes of light-grown genetic mutants of the AHLs and H2A.Z-exchanging components were suppressed by potent chemical inhibitors of auxin transport and YUC enzymes. These results suggest that the coordination of matrix attachment and chromatin modification underlies auxin biosynthesis in light-dependent hypocotyl growth.

Cuticular wax is an important hydrophobic layer that covers the plant aerial surface. Cuticular wax biosynthesis is shaped by multiple layers of regulation. In particular, a pair of R2R3-type MYB transcription factors, MYB96 and MYB30, are known to be the main participants in cuticular wax accumulation. Here, we report that the MYB30-INTERACTING E3 LIGASE 1 (MIEL1) E3 ubiquitin ligase controls the protein stability of the two MYB transcription factors and thereby wax biosynthesis in Arabidopsis. MIEL1-deficient miel1 mutants exhibit increased wax accumulation in stems, with up-regulation of wax biosynthetic genes targeted by MYB96 and MYB30. Genetic analysis reveals that wax accumulation of the miel1 mutant is compromised by myb96 or myb30 mutation, but MYB96 is mainly epistatic to MIEL1, playing a predominant role in cuticular wax deposition. These observations indicate that the MIEL1-MYB96 module is important for balanced cuticular wax biosynthesis in developing inflorescence stems., (© The Author 2017. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The circadian clock control of CONSTANS (CO) transcription and the light-mediated stabilization of its encoded protein coordinately adjust photoperiodic flowering by triggering rhythmic expression of the floral integrator flowering locus T (FT). Diurnal accumulation of CO is modulated sequentially by distinct E3 ubiquitin ligases, allowing peak CO to occur in the late afternoon under long days. Here we show that CO abundance is not simply targeted by E3 enzymes but is also actively self-adjusted through dynamic interactions between two CO isoforms. Alternative splicing of CO produces two protein variants, the full-size COα and the truncated COβ lacking DNA-binding affinity. Notably, COβ, which is resistant to E3 enzymes, induces the interaction of COα with CO-destabilizing E3 enzymes but inhibits the association of COα with CO-stabilizing E3 ligase. These observations demonstrate that CO plays an active role in sustaining its diurnal accumulation dynamics during Arabidopsis photoperiodic flowering., (© 2016 The Authors The Plant Journal © 2016 John Wiley & Sons Ltd.)

The phytohormone abscisic acid (ABA) regulates plant responses to various environmental challenges. Controlled protein turnover is an important component of ABA signalling. Here we show that the RING-type E3 ligase MYB30-INTERACTING E3 LIGASE 1 (MIEL1) regulates ABA sensitivity by promoting MYB96 turnover in Arabidopsis. Germination of MIEL1-deficient mutant seeds is hypersensitive to ABA, whereas MIEL1-overexpressing transgenic seeds are less sensitive. MIEL1 can interact with MYB96, a regulator of ABA signalling, and stimulate its ubiquitination and degradation. Genetic analysis shows that MYB96 is epistatic to MIEL1 in the control of ABA sensitivity in seeds. While MIEL1 acts primarily via MYB96 in seed germination, MIEL1 regulates protein turnover of both MYB96 and MYB30 in vegetative tissues. We find that ABA regulates the expression of MYB30-responsive genes during pathogen infection and this regulation is partly dependent on MIEL1. These results suggest that MIEL1 may facilitate crosstalk between ABA and biotic stress signalling.

In higher plants, shoot apical meristem (SAM) maintains cell division activity in order to give rise to aerial plant organs. Several lines of evidence have suggested that plants ensure stem cell proliferation activity in response to various external stimuli, thereby contributing to plant adaptation and fitness. Here, we report that the abscisic acid (ABA)-inducible R2R3-type MYB96 transcription factor regulates transcript accumulation of SHOOT MERISTEMLESS (STM) possibly to contribute to plant adaptation to environmental stress. STM was up-regulated in MYB96-overexpressing activation-tagging myb96-ox plants, but down-regulated in MYB96-deficient myb96-1 mutant plants, even in the presence of ABA. Notably, the MYB96 transcription factor bound directly to the STM promoter. In addition, consistent with the role of MYB96 in drought tolerance, transgenic plants overexpressing STM (35S:STM-MYC) were more tolerant to drought stress. These observations suggest that the MYB96-STM module contributes to enhancing plant tolerance to drought stress., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Plant cells have a remarkable ability to induce pluripotent cell masses and regenerate whole plant organs under the appropriate culture conditions. Although the in vitro regeneration system is widely applied to manipulate agronomic traits, an understanding of the molecular mechanisms underlying callus formation is starting to emerge. Here, we performed genome-wide transcriptome profiling of wild-type leaves and leaf explant-derived calli for comparison and identified 10,405 differentially expressed genes (> two-fold change). In addition to the well-defined signaling pathways involved in callus formation, we uncovered additional biological processes that may contribute to robust cellular dedifferentiation. Particular emphasis is placed on molecular components involved in leaf development, circadian clock, stress and hormone signaling, carbohydrate metabolism, and chromatin organization. Genetic and pharmacological analyses further supported that homeostasis of clock activity and stress signaling is crucial for proper callus induction. In addition, gibberellic acid (GA) and brassinosteroid (BR) signaling also participates in intricate cellular reprogramming. Collectively, our findings indicate that multiple signaling pathways are intertwined to allow reversible transition of cellular differentiation and dedifferentiation.

Chromatin structure determines the accessibility of transcriptional regulators to target DNA and contributes to regulation of gene expression. Posttranslational modifications of core histone proteins underlie the reversible changes in chromatin structure. Epigenetic regulation is closely associated with cellular differentiation. Consistently, we found that histone deacetylation is required for callus formation from leaf explants in Arabidopsis . Treatment with trichostatin A (TSA) led to defective callus formation on callus-inducing medium (CIM). Gene expression profiling revealed that a subset of HDAC genes, including HISTONE DEACETYLASE 9 (HDA9), HD-TUINS PROTEIN 1 (HDT1), HDT2, HDT4, and SIRTUIN 1 (SRT1), was significantly up-regulated in calli. In support of this, genetic mutations of HDA9 or HDT1 showed reduced capability of callus formation, probably owing to their roles in regulating auxin and embryonic and meristematic developmental signaling. Taken together, our findings suggest that histone deacetylation is intimately associated with the leaf-to-callus transition, and multiple signaling pathways are controlled by means of histone modification during cellular dedifferentiation., (Copyright © 2015 Elsevier GmbH. All rights reserved.)

Circadian clocks regulate the rhythms of biological activities with a period of approximately 24-hours and synchronize plant metabolism and physiology with the environmental cycles. The clock also gates responses to environmental stresses to maximize fitness advantages. Here we report that the MYB96 transcription factor is connected with the clock oscillator to shape the circadian gating of abscisic acid (ABA) responses. MYB96 directly binds to the TIMING OF CAB EXPRESSION 1 (TOC1) promoter to positively regulate its expression. The use of myb96 mutant plants shows that this regulation is essential for the gated induction of TOC1 by ABA. In turn, MYB96 induction by ABA is also altered in toc1-3 mutant plants. The increased tolerance to drought of MYB96 over-expressing plants is decreased in the toc1-3 mutant background, suggesting that MYB96 and TOC1 intersect the circadian clock and ABA signaling. The MYB96-TOC1 function might be also regulated by the clock component CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1), which binds to the MYB96 promoter and alters its circadian expression. Thus, a complex circuitry of CCA1-MYB96-TOC1 regulatory interactions provides the mechanistic basis underlying the connection between circadian and stress signaling to optimize plant fitness to ambient stresses.

Flowering is crucial for achieving reproductive success. A large number of well-delineated factors affecting flowering are involved in complex genetic networks in Arabidopsis thaliana. However, the underlying part played by the WRKY transcription factors in this process is not yet clear. Here, we report that WRKY71 is able to accelerate flowering in Arabidopsis. An activation-tagged mutant WRKY71-1D and a constitutive over-expresser of WRKY71 both flowered earlier than the wild type (WT). In contrast, both the RNA interference-based multiple WRKY knock-out mutant (w71w8 + 28RNAi) and the dominant repression line (W71-SRDX) flowered later. Gene expression analysis showed that the transcript abundance of the flowering time integrator gene FLOWERING LOCUS T (FT) and the floral meristem identity genes LEAFY (LFY), APETALA1 (AP1) and FRUITFULL (FUL) were greater in WRKY71-1D than in the WT, but lower in w71w8 + 28RNAi and W71-SRDX. Further, WRKY71 was shown to bind to the W-boxes in the FT and LFY promoters in vitro and in vivo. The suggestion is that WRKY71 activity hastens flowering via the direct activation of FT and LFY., (© 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.)

Background and Aim: The biosimilar of infliximab, CT-P13, has recently been shown to be equivalent to infliximab in both efficacy and safety in the treatment of rheumatologic diseases. However, no data are available with respect to the drug's efficacy in patients with inflammatory bowel disease (IBD). We aimed to assess the efficacy and safety of CT-P13 in IBD patients, Methods: This was a retrospective multicenter study including both anti-tumor necrosis factor (TNF) naïve patients and patients who switched from the biologic originator to CT-P13., Results: In anti-TNF naïve Crohn's disease (CD) patients (n = 32), clinical response and remission rates were 90.6% and 68.8% at week 2, 90.6% and 84.4% at week 8, 95.5% and 77.3% at week 30, and 87.5% and 75.0% at week 54, respectively. In anti-TNF naïve ulcerative colitis (UC) patients (n = 42), clinical response and remission rates were 76.2% and 19.0% at week 2, 81.0% and 38.1% at week 8, 91.3% and 47.8% at week 30, and 100% and 50.0% at week 54, respectively, while mucosal healing rates were 58.3% at week 8, 66.7% at week 30, and 66.7% at week 54. The efficacy of CT-P13 was maintained in 92.6% (25/27) of CD patients and in 66.7% (6/9) of UC patients after switching from its originator. Adverse events related to CT-P13 occurred in 11.8% of UC patients., Conclusions: CT-P13 appears to have comparable efficacy, safety, and interchangeability with its originator in the treatment of IBD. Further prospective studies with long-term follow-up periods will be needed to confirm the biosimilarity of CT-P13., (© 2015 Journal of Gastroenterology and Hepatology Foundation and Wiley Publishing Asia Pty Ltd.)

In plants, necrotic lesions occur at the site of pathogen infection through the hypersensitive response, which is followed by induction of systemic acquired resistance (SAR) in distal tissues. Salicylic acid (SA) induces SAR by activating NONEXPRESSER OF PATHOGENESIS-RELATED GENES1 (NPR1) through an oligomer-to-monomer reaction. However, SA biosynthesis is elevated only slightly in distal tissues during SAR, implying that SA-mediated induction of SAR requires additional factors. Here, we demonstrated that SA-independent systemic signals induce a gene encoding SNF1-RELATED PROTEIN KINASE 2.8 (SnRK2.8), which phosphorylates NPR1 during SAR. The SnRK2.8-mediated phosphorylation of NPR1 is necessary for its nuclear import. Notably, although SnRK2.8 transcription and SnRK2.8 activation are independent of SA signaling, the SnRK2.8-mediated induction of SAR requires SA. Together with the SA-mediated monomerization of NPR1, these observations indicate that SA signals and SnRK2.8-mediated phosphorylation coordinately function to activate NPR1 via a dual-step process in developing systemic immunity in Arabidopsis thaliana., (© 2015 American Society of Plant Biologists. All rights reserved.)

Floral transition is influenced by environmental factors such as light and temperature. Plants are capable of integrating photoperiod and ambient temperature signaling into their developmental program. Despite extensive investigations on individual genetic pathways, little is known about the molecular components that integrate both pathways. Here, we demonstrate that the RING finger-containing E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) acts as an integrator of photoperiod and ambient temperature signaling. In addition to the role in photoperiodic destabilization of CONSTANS (CO), COP1 also regulates temperature sensitivity by controlling the degradation of GIGANTEA (GI). COP1-impaired mutants showed reduced sensitivity to low ambient temperature. Notably, COP1 is more stabilized at low temperature and accelerates GI turnover in a 26S proteasome-dependent manner. The direct association of GI with the promoter of FLOWERING LOCUS T (FT) was reduced because of its ambient temperature-dependent protein stability control, and thus COP1-triggered GI turnover delays flowering at low temperatures via a CO-independent pathway. Taken together, our findings indicate that environmental conditions regulate the stability of COP1, and conditional specificity of its target selection stimulates proper developmental responses and ensures reproductive success.

Various environmental stresses limit plant growth, development, and reproductive success. Plants have therefore evolved sophisticated adaptive responses to deal with environmental challenges. The responses of plants to environmental stresses are mainly mediated by abscisic acid (ABA)-dependent and ABA-independent signaling pathways. While these two pathways have been implicated to play discrete roles in abiotic stress responses, accumulating evidence suggests that they are also intertwined. Here, we report that an R2R3-type MYB transcription factor, MYB96, integrates the ABA and cold signaling pathways. In addition to its role in ABA-mediated drought responses, MYB96 is also induced by cold stress in an ABA-independent manner and subsequently activates freezing tolerance. Notably, MYB96 regulates HEPTAHELICAL PROTEIN (HHP) genes by binding to their promoters. The HHP proteins, in turn, interact with C-REPEAT BINDING FACTOR (CBF) upstream regulators, such as INDUCER OF CBF EXPRESSION 1 (ICE1), ICE2, and CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3). The specific interactive networks of HHPs with the CBF upstream regulators are necessary to facilitate transcriptional activation of the CBF regulon under stressful conditions. Together, the MYB96-HHP module integrates ABA-dependent and ABA-independent signals and activates the CBF pathway, ensuring plant adaptation to a wide range of adverse environmental fluctuations., (© 2015 The Authors The Plant Journal © 2015 John Wiley & Sons Ltd.)

Seed germination is a key developmental transition that initiates the plant life cycle. The timing of germination is determined by the coordinated action of two phytohormones, gibberellin and abscisic acid (ABA). In particular, ABA plays a key role in integrating environmental information and inhibiting the germination process. The utilization of embryonic lipid reserves contributes to seed germination by acting as an energy source, and ABA suppresses lipid degradation to modulate the germination process. Here, we report that the ABA-responsive R2R3-type MYB transcription factor MYB96, which is highly expressed in embryo, regulates seed germination by controlling the expression of abscisic acid-insensitive4 (ABI4) in Arabidopsis (Arabidopsis thaliana). In the presence of ABA, germination was accelerated in MYB96-deficient myb96-1 seeds, whereas the process was significantly delayed in MYB96-overexpressing activation-tagging myb96-ox seeds. Consistently, myb96-1 seeds degraded a larger extent of lipid reserves even in the presence of ABA, while reduced lipid mobilization was observed in myb96-ox seeds. MYB96 directly regulates ABI4, which acts as a repressor of lipid breakdown, to define its spatial and temporal expression. Genetic analysis further demonstrated that ABI4 is epistatic to MYB96 in the control of seed germination. Taken together, the MYB96-ABI4 module regulates lipid mobilization specifically in the embryo to ensure proper seed germination under suboptimal conditions., (© 2015 American Society of Plant Biologists. All Rights Reserved.)

Background: Sugar plays a central role as a source of carbon metabolism and energy production and a signaling molecule in diverse growth and developmental processes and environmental adaptation in plants. It is known that sugar metabolism and allocation between different physiological functions is intimately associated with flowering transition in many plant species. The INDETERMINATE DOMAIN (IDD)-containing transcription factor IDD8 regulates flowering time by modulating sugar metabolism and transport under sugar-limiting conditions in Arabidopsis. Meanwhile, it has been reported that SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE 1 (SnRK1), which acts as a sensor of cellular energy metabolism, is activated by sugar deprivation. Notably, SnRK1-overexpressing plants and IDD8-deficient mutants exhibit similar phenotypes, including delayed flowering, suggesting that SnRK1 is involved in the IDD8-mediated metabolic control of flowering., Results: We examined whether the sugar deprivation-sensing SnRK1 is functionally associated with IDD8 in flowering time control through biochemical and molecular genetic approaches. Overproduction of AKIN10, the catalytic subunit of SnRK1, delayed flowering in Arabidopsis, as was observed in IDD8-deficient idd8-3 mutant. We found that AKIN10 interacts with IDD8 in the nucleus. Consequently, AKIN10 phosphorylates IDD8 primarily at two serine (Ser) residues, Ser-178 and Ser-182, which reside in the fourth zinc finger (ZF) domain that mediates DNA binding and protein-protein interactions. AKIN10-mediated phosphorylation did not affect the subcellular localization and DNA-binding property of IDD8. Instead, the transcriptional activation activity of the phosphorylated IDD8 was significantly reduced. Together, these observations indicate that AKIN10 antagonizes the IDD8 function in flowering time control, a notion that is consistent with the delayed flowering phenotypes of AKIN10-overexpressing plants and idd8-3 mutant., Conclusion: Our data show that SnRK1 and its substrate IDD8 constitute a sugar metabolic pathway that mediates the timing of flowering under sugar deprivation conditions. In this signaling scheme, the SnRK1 signals are directly integrated into the IDD8-mediated gene regulatory network that governs flowering transition in response to fluctuations in sugar metabolism, further supporting the metabolic control of flowering.

The circadian clock is a timekeeper mechanism that is able to regulate biological activities with a period of 24h. Proper matching of the internal circadian time with the environment not only confers fitness advantages but also allows the clock to temporally gate the responses to environmental stresses. By restricting the time of maximal responsiveness, the circadian gating defines an efficient way to increase resistance to stress without substantially decreasing plant growth. Stress signaling in turn appears to influence the clock activity. The feedback regulation might be important to maximize metabolic efficiency under challenging environmental conditions. This review focuses on recent research advances exploring the intricate connection between the clock and osmotic stresses. The role of the circadian clock favoring the proper balance between immune responses and cellular metabolism is also discussed., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Seed dormancy facilitates to endure environmental disadvantages by confining embryonic growth until the seeds encounter favorable environmental conditions for germination. Abscisic acid (ABA) and gibberellic acid (GA) play a pivotal role in the determination of the seed dormancy state. ABA establishes seed dormancy, while GA triggers seed germination. Here, we demonstrate that MYB96 contributes to the fine-tuning of seed dormancy regulation through the coordination of ABA and GA metabolism. The MYB96-deficient myb96-1 seeds germinated earlier than wild-type seeds, whereas delayed germination was observed in the activation-tagging myb96-1D seeds. The differences in germination rate disappeared after stratification or after-ripening. The MYB96 transcription factor positively regulates ABA biosynthesis genes 9-CIS-EPOXYCAROTENOID DIOXYGENASE 2 (NCED2), NCED5, NCED6, and NCED9, and also affects GA biosynthetic genes GA3ox1 and GA20ox1. Notably, MYB96 directly binds to the promoters of NCED2 and NCED6, primarily modulating ABA biosynthesis, which subsequently influences GA metabolism. In agreement with this, hyperdormancy of myb96-1D seeds was recovered by an ABA biosynthesis inhibitor fluridone, while hypodormancy of myb96-1 seeds was suppressed by a GA biosynthesis inhibitor paclobutrazol (PAC). Taken together, the metabolic balance of ABA and GA underlies MYB96 control of primary seed dormancy.

Ethylene regulates a variety of physiological processes, such as flowering, senescence, abscission, and fruit ripening. In particular, leaf expansion is also controlled by ethylene in Arabidopsis. Exogenous treatment with ethylene inhibits leaf expansion, and consistently, ethylene insensitive mutants show increased leaf area. Here, we report that the RING finger-containing E3 ubiquitin ligase HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1 (HOS1) regulates leaf expansion in an ethylene signaling pathway. The HOS1-deficient mutant showed reduced leaf area and was insensitive to ethylene perception inhibitor, silver thiosulfate (STS). Accordingly, genes encoding ethylene signaling components were significantly up-regulated in hos1-3. This study demonstrates that the HOS1 protein is involved in ethylene signal transduction for the proper regulation of leaf expansion possibly under environmentally stressful conditions.

The circadian clock is a biological time keeper mechanism that regulates biological rhythms to a period of approximately 24 h. The circadian clock enables organisms to anticipate environmental cycles and coordinates internal cellular physiology with external environmental cues. In plants, correct matching of the clock with the environment confers fitness advantages to plant survival and reproduction. Therefore, circadian clock components are regulated at multiple layers to fine-tune the circadian oscillation. Epigenetic regulation provides an additional layer of circadian control. However, little is known about which chromatin remodeling factors are responsible for circadian control. In this work, we analyzed circadian expression of 109 chromatin remodeling factor genes and identified 17 genes that display circadian oscillation. In addition, we also found that a candidate interacts with a core clock component, supporting that clock activity is regulated in part by chromatin modification. As an initial attempt to elucidate the relationship between chromatin modification and circadian oscillation, we identified novel regulatory candidates that provide a platform for future investigations of chromatin regulation of the circadian clock.

The transition between seed dormancy and germination is an important stage that initiates plant life cycle. Hormonal balances of abscisic acid (ABA) and gibberellin (GA) contribute to determining the proper timing to germinate. Here, we demonstrate that the R2R3-type MYB96 transcription factor, a key ABA signaling mediator, coordinates seed dormancy and germination processes through distinct downstream events. This transcription factor controls ABA-INSENSITIVE 4 (ABI4) expression to inhibit seed germination by suppressing breakdown of lipid reserves in embryo. In addition, it also induces seed dormancy by stimulating ABA biosynthesis in an ABI4-independent manner. We propose that MYB96 integrates a multitude of environmental stress signals and acts as a master regulator in the determination of timing for seed germination.

In the title compound, C18H17FO2S, the dihedral angle between the plane of the benzo-furan ring system (r.m.s. deviation = 0.013 Å) and that of the 4-fluoro-phenyl ring is 74.30 (5)°. In the crystal, weak C-H⋯O and C-H⋯F hydrogen bonds link the mol-ecules into columns extending in direction [100].

In the title compound, C17H15BrO2S, the dihedral angle between the plane of the benzo-furan ring system [r.m.s. deviation = 0.004 (3) Å] and that of the 4-methyl-phenyl ring is 0.9 (2)°. In the crystal, mol-ecules are linked by C-H⋯O, C-H⋯π and Br⋯π [3.636 (2) Å] inter-actions, and by π-π inter-actions between the 4-methyl-phenyl and furan rings of neighbouring mol-ecules [centroid-centroid distance = 3.650 (2) Å], forming a three-dimensional network.

In the title compound, C15H10F2O2S, the dihedral angle between the plane of the benzo-furan ring system (r.m.s. deviation = 0.015 Å) and that of the 2-fluoro-phenyl ring is 28.53 (6)°. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯F hydrogen bonds, and by π-π inter-actions between the furan and benzene rings of neighbouring mol-ecules [centroid-centroid distance = 3.625 (2) Å], forming a three-dimensional network.

In the title compound, C21H22O3S, the cyclo-pentyl ring adopts a twist conformation. The dihedral angle between the mean planes of the benzo-furan and 4-methyl-phenyl rings is 72.38 (6)°. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯π inter-actions, forming a three-dimensional supra-molecular network.

In the title compound, C17H15BrO3S, the dihedral angle between the mean planes of the benzo-furan and 3-methyl-phenyl rings is 77.37 (5)°. In the crystal, mol-ecules are linked via pairs of Br⋯O [Br⋯O = 3.335 (2) Å] contacts into inversion dimers. These dimers are further linked by C-H⋯O hydrogen bonds and π-π inter-actions between the benzene and furan rings of neighbouring mol-ecules [centroid-centroid separation = 3.884 (3) Å] into supra-molecular chains running along the a-axis direction.

In the title compound, C17H15ClO3S, the dihedral angle between the mean planes of the benzo-furan and 3-methyl-phenyl rings is 76.99 (4)°. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds into chains along the b-axis direction. These chains are linked by π-π inter-actions between the benzene and furan rings of neighbouring mol-ecules [centroid-centroid distance = 3.976 (2) Å].