Regulatory Mechanisms of Transcription Factors in Plant Morphology and Function 2.0.

In plants, gene regulation underlies organ development and responses to environmental changes [...].

Regulatory Mechanisms of Transcription Factors in Plant Morphology and Function.

Plants develop organs such as flowers and leaves with different morphologies [...].

Transgenic Forsythia plants expressing sesame cytochrome P450 produce beneficial lignans.

Lignans are widely distributed plant secondary metabolites that have received attention for their benefits to human health. Sesamin is a furofran lignan that is conventionally extracted from Sesamum seeds and shows anti-oxidant and anti-inflammatory activities in the human liver. Sesamin is biosynthesized by the Sesamum-specific enzyme CYP81Q1, and the natural sources of sesamin are annual plants that are at risk from climate change. In contrast, Forsythia species are widely distributed perennial woody plants that highly accumulate the precursor lignan pinoresinol. To sustainably supply sesamin, we developed a transformation method for Forsythia leaf explants and generated transgenic Forsythia plants that heterologously expressed the CYP81Q1 gene. High-performance liquid chromatography (HPLC) and LC-mass spectrometry analyses detected sesamin and its intermediate piperitol in the leaves of two independent transgenic lines of F. intermedia and F. koreana. We also detected the accumulation of sesamin and piperitol in their vegetatively propagated descendants, demonstrating the stable and efficient production of these lignans. These results indicate that CYP81Q1-transgenic Forsythia plants are promising prototypes to produce diverse lignans and provide an important strategy for the cost-effective and scalable production of lignans.

CIN-like TCP13 is essential for plant growth regulation under dehydration stress.

KEY MESSAGE: A dehydration-inducible Arabidopsis CIN-like TCP gene, TCP13, acts as a key regulator of plant growth in leaves and roots under dehydration stress conditions. Plants modulate their shape and growth in response to environmental stress. However, regulatory mechanisms underlying the changes in shape and growth under environmental stress remain elusive. The CINCINNATA (CIN)-like TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) family of transcription factors (TFs) are key regulators for limiting the growth of leaves through negative effect of auxin response. Here, we report that stress-inducible CIN-like TCP13 plays a key role in inducing morphological changes in leaves and growth regulation in leaves and roots that confer dehydration stress tolerance in Arabidopsis thaliana. Transgenic Arabidopsis plants overexpressing TCP13 (35Spro::TCP13OX) exhibited leaf rolling, and reduced leaf growth under osmotic stress. The 35Spro::TCP13OX transgenic leaves showed decreased water loss from leaves, and enhanced dehydration tolerance compared with their control counterparts. Plants overexpressing a chimeric repressor domain SRDX-fused TCP13 (TCP13pro::TCP13SRDX) showed severely serrated leaves and enhanced root growth. Transcriptome analysis of TCP13pro::TCP13SRDX transgenic plants revealed that TCP13 affects the expression of dehydration- and abscisic acid (ABA)-regulated genes. TCP13 is also required for the expression of dehydration-inducible auxin-regulated genes, INDOLE-3-ACETIC ACID5 (IAA5) and LATERAL ORGAN BOUNDARIES (LOB) DOMAIN 1 (LBD1). Furthermore, tcp13 knockout mutant plants showed ABA-insensitive root growth and reduced dehydration-inducible gene expression. Our findings provide new insight into the molecular mechanism of CIN-like TCP that is involved in both auxin and ABA response under dehydration stress.

Author Correction: Identification of a binding protein for sesamin and characterization of its roles in plant growth.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Author Correction: Identification of a binding protein for sesamin and characterization of its roles in plant growth.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Practical optimization of liquid chromatography/mass spectrometry conditions and pretreatment methods toward the sensitive quantification of auxin in plants.

RATIONALE: The plant hormone auxin, indole-3-acetic acid, regulates many aspects of plant growth and development. Auxin quantification should offer broad insights into its mechanistic action in plants. However, limited auxin content in plant tissues hampers the establishment of quantification methods without the highest graded instruments or deeply specialized experimental techniques. METHODS: In this study, we detailed optimized conditions for high-performance liquid chromatography coupled with triple-quadrupole mass spectrometry (LC/MS). We compared LC/MS conditions, such as columns, mobile phases, parameters of acquisition methods (selective or multiple ion monitoring), dwell times (DTs), and channel numbers, using differentially mixed authentic auxin and its related compounds. We further investigated pretreatment methods through the optimization of auxin recovery and irrelative compound removal from plant tissues prior to the LC/MS analysis. RESULTS: Our LC/MS analysis demonstrated the particular importance of the column, DTs, and channel numbers on detection sensitivity. Our comparative analysis developed optimal pretreatment methods, including the pulverization of plants, concentration of extract through centrifugal evaporation, and removal of irrelative metabolites using liquid-liquid extraction and a spin filter. We injected plant samples into our LC/MS system, quantified auxin and eight related compounds in a single measurement, and determined the auxin increase in an auxin over-producing mutant. CONCLUSIONS: Our practical optimization of LC/MS conditions and pretreatment methods provides detailed experimental processes toward the sensitive quantification of auxin from 10 mg of plant tissue. These processes have not always been clearly documented; therefore, our protocol could broadly contribute to technical advances in plant growth and development research.

Identification of a binding protein for sesamin and characterization of its roles in plant growth.

Sesamin is a furofuran-type lignan that is found abundantly in seeds of Sesamum indicum (sesame) and has been widely accepted as a dietary supplement with positive effects on human health. The biological activity of sesamin in human cells and organs has been analysed extensively, although comparatively few studies show biological functions for sesamin in planta. Herein we screened sesamin-binding proteins (SBP) from sesame seedling extracts using sesamin-immobilized nano-beads. In subsequent peptide mass fingerprinting analyses, we identified a SBP, Steroleosin B, which is one of the membrane proteins found in oil bodies. In addition, pull-down assays and saturation transfer difference-nuclear magnetic resonance (STD-NMR) experiments demonstrated that sesamin binds directly to recombinant Steroleosin B in vitro. Finally, ectopic accumulations of sesamin and Steroleosin B in transgenic Arabidopsis thaliana plants induced severe growth defects including suppression of leaf expansion and root elongation. Collectively, these results indicate that sesamin influences tissue development in the presence of Steroleosin B.

A hidden link between leaf development and senescence.

Leaf senescence is the final step of leaf development and is usually accompanied by visible color changes from green to yellow or brown. Unlike the senescence of the whole body of animals and unicellular organisms, which is often associated with death, leaf senescence in plants requires highly integrative processes towards cell death with nutrient recycling and storage. Since leaf senescence plays pivotal roles in the production of plant biomass and grain yield, the mechanisms of degradation and relocation of macromolecules as well as the regulation of signaling and biosynthetic pathways have received much attention. The importance of the plant hormone ethylene in the onset of leaf senescence has been clearly documented. However, research has increasingly demonstrated that the function of ethylene in the regulation of leaf senescence is dependent on leaf development. This review raises the issue of how ethylene requires developmental regulators and focuses on the developmental aspect of leaf senescence. It also emphasizes the remarkable impact that developmental regulators have on regulating the onset of leaf senescence.

The function of ETHYLENE RESPONSE FACTOR genes in the light-induced anthocyanin production of Arabidopsis thaliana leaves.

Plants grow under threats of environmental changes that could injure cellular viability and damage whole-plant physiology. To defend themselves against such threats, plants induce protective responses, including the production of defense molecules. The red/purple pigment anthocyanin is synthesized upon leaf and fruit development as well as environmental stimuli such as excess light exposure. Therefore, the anthocyanin biosynthesis is considered as a model signaling pathway of the integration of developmental and environmental responses. This integration is tightly regulated by transcription factors, but the integrative mode of these signaling pathways has received little attention. In this study, using an Arabidopsis mutant with mutation in two ETHYLENE RESPONSE FACTOR (ERF) genes, AtERF4 and AtERF8, we investigated the regulatory signaling pathway that leads to the production of anthocyanin in response to light. We detected the accumulation of anthocyanin in detached leaves after incubation on water under light illumination and intact leaves after being transferred into the strong light condition, suggesting that the photoinhibition mediated the production of anthocyanin. Our results demonstrated that the erf mutant decreased the rate and extent of the production of anthocyanin in association with changes of the transcript levels of anthocyanin-biosynthetic genes. As these ERF genes are known regulators of leaf senescence-the final stage of leaf development-we provide an insight into the ERF-mediated integration of two regulatory pathways of the light response and developmental age.

Roles of miR319 and TCP Transcription Factors in Leaf Development.

Sophisticated regulation of gene expression, including microRNAs (miRNAs) and their target genes, is required for leaf differentiation, growth, and senescence. The impact of miR319 and its target TEOSINTE BRANCHED1, CYCLOIDEA, and PROLIFERATING CELL NUCLEAR ANTIGEN BINDING FACTOR (TCP) genes on leaf development has been extensively investigated, but the redundancies of these gene families often interfere with the evaluation of their function and regulation in the developmental context. Here, we present the genetic evidence of the involvement of the MIR319 and TCP gene families in Arabidopsis (Arabidopsis thaliana) leaf development. Single mutations in MIR319A and MIR319B genes moderately inhibited the formation of leaf serrations, whereas double mutations increased the extent of this inhibition and resulted in the formation of smooth leaves. Mutations in MIR319 and gain-of-function mutations in the TCP4 gene conferred resistance against miR319 and impaired the cotyledon boundary and leaf serration formation. These mutations functionally associated with CUP-SHAPED COTYLEDON genes, which regulate the cotyledon boundary and leaf serration formation. In contrast, loss-of-function mutations in miR319-targeted and nontargeted TCP genes cooperatively induced the formation of serrated leaves in addition to changes in the levels of their downstream gene transcript. Taken together, these findings demonstrate that the MIR319 and TCP gene families underlie robust and multilayer control of leaf development. This study also provides a framework toward future researches on redundant miRNAs and transcription factors in Arabidopsis and crop plants.

TCP4-dependent induction of CONSTANS transcription requires GIGANTEA in photoperiodic flowering in Arabidopsis.

Photoperiod is one of the most reliable environmental cues for plants to regulate flowering timing. In Arabidopsis thaliana, CONSTANS (CO) transcription factor plays a central role in regulating photoperiodic flowering. In contrast to posttranslational regulation of CO protein, still little was known about CO transcriptional regulation. Here we show that the CINCINNATA (CIN) clade of class II TEOSINTE BRANCHED 1/ CYCLOIDEA/ PROLIFERATING CELL NUCLEAR ANTIGEN FACTOR (TCP) proteins act as CO activators. Our yeast one-hybrid analysis revealed that class II CIN-TCPs, including TCP4, bind to the CO promoter. TCP4 induces CO expression around dusk by directly associating with the CO promoter in vivo. In addition, TCP4 binds to another flowering regulator, GIGANTEA (GI), in the nucleus, and induces CO expression in a GI-dependent manner. The physical association of TCP4 with the CO promoter was reduced in the gi mutant, suggesting that GI may enhance the DNA-binding ability of TCP4. Our tandem affinity purification coupled with mass spectrometry (TAP-MS) analysis identified all class II CIN-TCPs as the components of the in vivo TCP4 complex, and the gi mutant did not alter the composition of the TCP4 complex. Taken together, our results demonstrate a novel function of CIN-TCPs as photoperiodic flowering regulators, which may contribute to coordinating plant development with flowering regulation.

Generation of Triple-Transgenic Forsythia Cell Cultures as a Platform for the Efficient, Stable, and Sustainable Production of Lignans.

Sesamin is a furofuran lignan biosynthesized from the precursor lignan pinoresinol specifically in sesame seeds. This lignan is shown to exhibit anti-hypertensive activity, protect the liver from damages by ethanol and lipid oxidation, and reduce lung tumor growth. Despite rapidly elevating demand, plant sources of lignans are frequently limited because of the high cost of locating and collecting plants. Indeed, the acquisition of sesamin exclusively depends on the conventional extraction of particular Sesamum seeds. In this study, we have created the efficient, stable and sustainable sesamin production system using triple-transgenic Forsythia koreana cell suspension cultures, U18i-CPi-Fk. These transgenic cell cultures were generated by stably introducing an RNAi sequence against the pinoresinol-glucosylating enzyme, UGT71A18, into existing CPi-Fk cells, which had been created by introducing Sesamum indicum sesamin synthase (CYP81Q1) and an RNA interference (RNAi) sequence against pinoresinol/lariciresinol reductase (PLR) into F. koreanna cells. Compared to its transgenic prototype, U18i-CPi-Fk displayed 5-fold higher production of pinoresinol aglycone and 1.4-fold higher production of sesamin, respectively, while the wildtype cannot produce sesamin due to a lack of any intrinsic sesamin synthase. Moreover, red LED irradiation of U18i-CPi-Fk specifically resulted in 3.0-fold greater production in both pinoresinol aglycone and sesamin than production of these lignans under the dark condition, whereas pinoresinol production was decreased in the wildtype under red LED. Moreover, we developed a procedure for sodium alginate-based long-term storage of U18i-CPi-Fk in liquid nitrogen. Production of sesamin in U18i-CPi-Fk re-thawed after six-month cryopreservation was equivalent to that of non-cryopreserved U18i-CPi-Fk. These data warrant on-demand production of sesamin anytime and anywhere. Collectively, the present study provides evidence that U18i-CP-Fk is an unprecedented platform for efficient, stable, and sustainable production of sesamin, and shows that a transgenic and specific light-regulated Forsythia cell-based metabolic engineering is a promising strategy for the acquisition of rare and beneficial lignans.

Essences in metabolic engineering of lignan biosynthesis.

Lignans are structurally and functionally diverse phytochemicals biosynthesized in diverse plant species and have received wide attentions as leading compounds of novel drugs for tumor treatment and healthy diets to reduce of the risks of lifestyle-related non-communicable diseases. However, the lineage-specific distribution and the low-amount of production in natural plants, some of which are endangered species, hinder the efficient and stable production of beneficial lignans. Accordingly, the development of new procedures for lignan production is of keen interest. Recent marked advances in the molecular and functional characterization of lignan biosynthetic enzymes and endogenous and exogenous factors for lignan biosynthesis have suggested new methods for the metabolic engineering of lignan biosynthesis cascades leading to the efficient, sustainable, and stable lignan production in plants, including plant cell/organ cultures. Optimization of light conditions, utilization of a wide range of elicitor treatments, and construction of transiently gene-transfected or transgenic lignan-biosynthesizing plants are mainly being attempted. This review will present the basic and latest knowledge regarding metabolic engineering of lignans based on their biosynthetic pathways and biological activities, and the perspectives in lignan production via metabolic engineering.

The roles of ethylene and transcription factors in the regulation of onset of leaf senescence.

Leaf senescence is the last stage of leaf development and is accompanied by cell death. In contrast to senescence in individual organisms that leads to death, leaf senescence is associated with dynamic processes that include the translocation of nutrients from old leaves to newly developing or storage tissues within the same plant. The onset of leaf senescence is largely regulated by age and internal and external stimuli, which include the plant hormone ethylene. Earlier studies have documented the important role of ethylene in the regulation of leaf senescence. The production of ethylene coincides with the onset of leaf senescence, whereas the application of ethylene to plants induces precocious leaf senescence. Recently, many studies have described the components of ethylene signaling and biosynthetic pathways that are involved in modulating the onset of leaf senescence. Particularly, transcription factors (TFs) integrate ethylene signals with those from environmental and developmental factors to accelerate or delay leaf senescence. This review aims to discuss the regulatory cascade involving ethylene and TFs in the regulation of onset of leaf senescence.

MIXTA-like transcription factors and WAX INDUCER1/SHINE1 coordinately regulate cuticle development in Arabidopsis and Torenia fournieri.

The waxy plant cuticle protects cells from dehydration, repels pathogen attack, and prevents organ fusion during development. The transcription factor WAX INDUCER1/SHINE1 (WIN1/SHN1) regulates the biosynthesis of waxy substances in Arabidopsis thaliana. Here, we show that the MIXTA-like MYB transcription factors MYB106 and MYB16, which regulate epidermal cell morphology, also regulate cuticle development coordinately with WIN1/SHN1 in Arabidopsis and Torenia fournieri. Expression of a MYB106 chimeric repressor fusion (35S:MYB106-SRDX) and knockout/down of MYB106 and MYB16 induced cuticle deficiencies characterized by organ adhesion and reduction of epicuticular wax crystals and cutin nanoridges. A similar organ fusion phenotype was produced by expression of a WIN1/SHN1 chimeric repressor. Conversely, the dominant active form of MYB106 (35S:MYB106-VP16) induced ectopic production of cutin nanoridges and increased expression of WIN1/SHN1 and wax biosynthetic genes. Microarray experiments revealed that MYB106 and WIN1/SHN1 regulate similar sets of genes, predominantly those involved in wax and cutin biosynthesis. Furthermore, WIN1/SHN1 expression was induced by MYB106-VP16 and repressed by MYB106-SRDX. These results indicate that the regulatory cascade of MIXTA-like proteins and WIN1/SHN1 coordinately regulate cutin biosynthesis and wax accumulation. This study reveals an additional key aspect of MIXTA-like protein function and suggests a unique relationship between cuticle development and epidermal cell differentiation.

A regulatory cascade involving class II ETHYLENE RESPONSE FACTOR transcriptional repressors operates in the progression of leaf senescence.

Leaf senescence is the final process of leaf development that involves the mobilization of nutrients from old leaves to newly growing tissues. Despite the identification of several transcription factors involved in the regulation of this process, the mechanisms underlying the progression of leaf senescence are largely unknown. Herein, we describe the proteasome-mediated regulation of class II ETHYLENE RESPONSE FACTOR (ERF) transcriptional repressors and involvement of these factors in the progression of leaf senescence in Arabidopsis (Arabidopsis thaliana). Based on previous results showing that the tobacco (Nicotiana tabacum) ERF3 (NtERF3) specifically interacts with a ubiquitin-conjugating enzyme, we examined the stability of NtERF3 in vitro and confirmed its rapid degradation by plant protein extracts. Furthermore, NtERF3 accumulated in plants treated with a proteasome inhibitor. The Arabidopsis class II ERFs AtERF4 and AtERF8 were also regulated by the proteasome and increased with plant aging. Transgenic Arabidopsis plants with enhanced expression of NtERF3, AtERF4, or AtERF8 showed precocious leaf senescence. Our gene expression and chromatin immunoprecipitation analyses suggest that AtERF4 and AtERF8 targeted the EPITHIOSPECIFIER PROTEIN/EPITHIOSPECIFYING SENESCENCE REGULATOR gene and regulated the expression of many genes involved in the progression of leaf senescence. By contrast, an aterf4 aterf8 double mutant exhibited delayed leaf senescence. Our results provide insight into the important role of class II ERFs in the progression of leaf senescence.